Typhaceae/Xyridaceae 461

Selected Bibliography

Celakovsky, L. 1885. Uber die Inflorescenz von Typha. Flora 68: 617-630.

Celakovsky, L. 1891. Uber die Verwandtschaft von Typha und Sparganium. bsterr. Bot. Z. 41: 117-121, 154-160, 195-199, 224-228,266-272.

Chase, M.W. et al. 1995. See general references. Cook, C.D.K., Nicholls, M.S. 1986/87. A monographic study of

the genus Sparganium (Sparganiaceae). Bot. Helv. 96: 213-267, 97: 1-44.

Davis, J .I. 1995. A phylogenetic structure for the mono­coyledons, as inferred from chloroplast DNA restriction site variation, and a comparison of measures of clade support. Syst. Bot. 20: 503-527.

Duvall, M.R. et al. 1993. Phylogenetic hypotheses for the monocotyledons reconstructed from rbcL sequence data. Ann. Mo. Bot. Gard. 80: 607-619.

Finlayson, C.M., Roberts, J., Chick, A.J., Sale, P.J.M. 1983. The biology of Australian weeds II. Typha dominguensis Pers. and Typha orienta/is Presl. J. Aust. Inst. Agric. Sci. 49:3-10.

Frolich, D., Barthlott, W. 1988. See general references. Harris, P.J., Hartley, R.D. 1980. See general references. Hegnauer, R. 1963, 1986. See general references. Herendeen, P.S., Crane, P.R. 1995. The fossil history of the

monocotyledons. In: Rudall, P.J., Cribb, P.J., Cutler, D.F., Humphries, C.J. (eds.) Monocotyledons: systematics and evolution. Royal Botanic Gardens, Kew, pp. 1-21.

Kaul, R.B. 1972. Adaptive leaf architecture in emergent and floating Sparganium. Am. J. Bot. 59: 270-278.

Kaul, R.B. 1976. Anatomical observations on floating leaves. Aquat. Bot. 2: 215-234.

Krattinger, K. 1978. Biosystematische Untersuchungen innerhalb der Gattung Typha L. Mitt. Bot. Mus. Univ. Ziirich 298. 270 pp.

Linder, P.H., Kellogg, E.A. 1995. Phylogenetic patterns in the commelinoid clade. In: Rudall, P.J., Cribb, P.J., Cutler, D.F., Humphries, C.J. (eds.) Monocotyledons: systematics and evolution. Royal Botanic Gardens, Kew, pp. 473-496.

Miiller-Doblies, D. 1970. Uber die Verwandtschaft von Typha und Sparganium im Infloreszenz- und Bliitenbau. Bot. Jahrb. Syst. 89: 451-562.

Miiller-Doblies, U. 1969. Uber die Bliitenstande und Bliiten sowie zur Embryologie von Sparganium. Bot. Jahrb. Syst. 89: 359-450.

Nicholls, M.S., Cook, C.D.K. 1986. The function of pollen tetrads in Typha (Typhaceae). VerOff. Geobot. Inst. ETH, Stiftung Riibel, Ziirich 97: 112-119.

Punt, W. 1975. The Northwest European pollen flora: 5. Sparganiaceae and Typhaceae. Rev. Palaeobot. Palynol. 19: 75-88.

Smith, S.G. 1987. Typha: its taxonomy and the ecological significance of hybrids. Arch. Hydrobiol. 27: 129-138.

Solereder, H., Mayer, F.J. 1933. Systematische Anatomie der Monokotylen. Heft I. Pandanales-Helobiae-Triuridales. 1. Teil. Typhaceae-Scheuchzeriaceae. Berlin: Borntraeger.

Thieret, J.W. 1982. The Sparganiaceae in the southeastern United States. J. Arnold Arbor. 63: 341-355.

Thieret, J.W., Luken, J.O. 1996. The Typhaceae in the south­eastern United States. Harvard Pap. Bot. 8: 27-56.

Yeo, R.R. 1964. Life history of the common cattail. Weeds. 12: 284-288.

Xyridaceae

R.KRAL

Xyridaceae C. Agardh, Aphor. Bot.: 158 (1823), nom. cons.

Rosulate to caulescent, low and delicate to tall and coarse, perennial to annual, terrestrial (rarely aquatic) herbs, mostly heliophytes of high­hydroperiod acidic soils. Roots mostly slender, diffuse-fibrous, with root hairs. Axis sympodial or monopodia!. Leaves alternate, distichous or spiral, ligulate or eligulate, the bases broad, open, sheath­ing, sheaths frequently equitant and keeled; blades laterally to dorsiventrally compressed, less often terete, angulate, or variously canaliculate. In­florescence lateral or terminal, scapose (rarely subsessile), the scapes 1-few from axils of scape sheaths or inner leaves, naked or with distant to approximate pairs of bracteal leaves, each scape bearing apically 1(-2) imbricate-bracted spikes or heads or a panicle of spikes. Flowers perfect, 1-many, solitary and subsessile in axils of chaffy, leathery or scarious bracts, or (Achlyphila) pedi­cellate in spathe axils; perianth in 2 differentiated whorls; sepals (2-)3, the anterior (inner) 1 a reduced scale, or subequal to the rest, or (Xyris) membranous and wrapped around the corolla, abcissing as the flower opens, the outer 2 subopposite, connivent to connate, chaffy, mostly navicular, often keeled, persistent around the ripe fruit; petals 3, equal or unequal, distinct to united, then salverform or bilabiate, mostly narrowed to claws or to a narrow tube; stamens 3( -6), oppositipetalous, borne upon the petals or hypo­gynous; anthers tetrasporangiate, basifixed, usu­ally bilocular at anthesis, introrsely or laterally dehiscent, dehiscing longitudinally; staminodia (1-)3, hypogynous to borne upon the petals, fila­mentous to bibrachiate and penicillate-hairy; gynoecium 3-carpellate, superior, the ovary 1-locular to completely or incompletely trilocular; placentation marginal, parietal, basal, free-central or axile (all conditions found in Xyris, in all other genera axile); style terminal, proximally terete to angled, slender, appendaged or exappendiculate, apically 3-branched to U-shaped stigmas, or vari­ously dilated to infundibular or laminar or subcapitate, usually papillate or fringed stigmatic zones. Fruit capsular, mostly loculicidal; seeds

K. Kubitzki (ed.), Flowering Plants · Monocotyledons© Springer-Verlag Berlin Heidelberg 1998

462 Xyridaceae

usually numerous, rarely 1, mostly with strong longitudinal ridges and finer cross-lines, translu­cent or farinose-opaque, the embryo small, situ­ated at base of or lateral to an abundant mealy (sometimes oily) endosperm.

An essentially pantropic family of five genera and over 300 species, most of them in Xyris, the only genus to occur in both New and Old Worlds, and to range into the north-temperate zone; the remaining four genera confined to S America.

VEGETATIVE MORPHOLOGY. The roots are fi­brous, diffuse, mostly filiform, less often fleshy. The rootstocks are commonly rhizomes, rarely bulbous; stems are usually short, less often elongate, sometimes caudiciform, sometimes stout and subligneous, mostly with contracted internodes.

The leaves are equitant and distichous in Achlyphila and in most Xyris, are polystichous in Abolboda, Aratitiyopea, Orectanthe and some Xyris; in all Abolboda, in Orectanthe sceptrum, in Aratitiyopea and in most Xyris a strong rosette is formed around a contracted stem or apically on vegetative shoots of a season. In more elongate­stemmed examples in Orectanthe they are in high spiral, or in Achlyphila and some Xyris, form long, frondlike plates of imbricate-based leaves and no rosette is evident. The leaf sheaths are open in all genera. In Achlyphila and most Xyris the blades are unifacial; in the other genera the blade is dor­siventrally compressed, often lingulate, variously tapering uninterruptedly from broad sheaths. In those Xyris in which the blade is not unifacial it is typically narrowly linear to filiform, terete, or angulate, variously canaliculate, particularly adaxially. In all genera save Xyris, even in most of these, the transition from sheath to blade is unin­terrupted, but in some Xyris there is a ligule or the scarious sheath border breaks into auricles at convergence of sheath and blade.

VEGETATIVE ANATOMY. Anatomical studies have been done on all genera except the recently de­scribed Aratitiyopea, these excellently detailed and summarized by Tomlinson (1969), whose source particularly for much information on Abolboda, Achlyphila, and Orectanthe was Carlquist (1960). Features shared by members of the Xyridaceae are: vessels with simple perfora­tion plates in roots, stems and leaves, and amphivasal vascular bundles in rhizome and/or stems. Most have irregular plates of stellate cells in the root cortex and a more or less uniform distri­bution of phloem through the root stele.

Fig. 114A-G. Xyridaceae. Abolboda ciliata. A Habit. B Spike. C Spread corolla with stamens and staminodes. D Stamen. E Pistil, note appendaged style. F Capsule (left), adaxial view of capsule valve (right). G Seed. (Kral1992)

The roots have an exodermis of one or more compact, lignosuberized layers under a larger­celled piliferous layer (or this lacking in Xyris brevifolia); root hairs mostly arising toward one end of an epidermal cell, sometimes in irregular vertical series. The middle cortex is frequently narrow, sometimes a single layer of cells (Abolboda, Xyris brevifolia); in Xyris it ranges from radial plates of cells separated by wide inter­cellular spaces to more uniform cortex. Some­times horizontal irregular plates of lobed or stellate cortical cells cut off from ends oflong cells to form irregular transverse diaphragms or an irregular reticulum. The endodermis incon­spicuous, of large and uniformly thickened cells (this thickening specific in degree and orienta­tion), usually of 1 layer but sometimes truly multiseriate. Stele usually narrow in comparison

Xyridaceae 463

to cortex. The pericycle consists of small, thin­walled cells, rarely or often interrupted by adja­cent vessels. The stele is diarch to polyarch with 2 or more peripheral vessels. Protoxylem is absent or present as isolated narrow elements. Phloem elements are mostly not grouped in peripheral phloem strands, but are scattered irregularly throughout the central ground tissue.

The rhizome or caudex, except in Achlyphila has short internodes, and in stocky-stemmed Abolboda, Orectanthe, it is subligneous. The surface layers are often suberized in Abolboda and Orectanthe, sometimes so in Xyris, and in Achlyphila they are thin-walled.

Leaf anatomy has been the most studied (see Arber 1922; Solereder and Meyer 1929; and Tomlinson 1969 for summaries). Epicuticular waxes are absent (Frolich and Barthlott 1988), but in one Xyris the leaf epidermis was found to be covered by a secretion deposited in droplets that could not be dissolved by organic solvents.

In Xyris the leaf blade epidermis is typically uni­form and the cells are longitudinally oriented and rectangular. There are many species in which outer walls are produced into papillae, tubercles, etc., in yet others the end walls are distinctly thickened and are variously cutinized. Epidermal sculpture may be useful taxonomically. In Achlyphila epidermal cell ends sometimes overlap at their narrowed ends, thus in cross-section the epidermis may appear biseriate; walls are much thickened, anticlinally conspicuously pitted and with transverse protuberances on end walls giving the blade an irregular epidermal outline. While the epidermis in some Abolboda (i.e. A. scabrida) may be produced into rugulosities or be papillose or scabrid, hairs are produced only in Xyris.

Hairs in Xyris may be uniseriate-glandular, short-unicellular and unbranched, or rarely branched (X. tenella, leaf sheath). In several spe­cies long hairs may be produced at sheath margins and many have ciliate or ciliate-scabrid blades. In some species the inner surface ofleaf sheaths may produce hairs or have secretory function.

In Achlyphila and most Xyris stomata are found on both sides of the lamina; in the other genera they are strictly abaxial. In all genera studied, guard cells are not sunken and are similar in con­figuration as are lateral subsidiary cells. Terminal subsidiary cells are not developed except in some Abolboda.

The hypodermis is well developed in Orectanthe and most Abolboda; in Xyris it is lacking, though in some there may be a distinct palisade of anticlinally elongate cells, and in Achlyphila this

might be a chlorenchymatous layer, including palisade.

The mesophyll of most Xyris is uniform, and the cells adjacent to substomatal chambers are often L-shaped. In a few species the mesophyll may be of elongate, lobed cells with lobes connivent at the tip and in thick or terete-bladed species the central mesophyll may be of large colorless cells which may break to produce 1 or more longitudinal air canals. In Achlyphila the mesophyll has a periph­eral chlorenchymatous layer and a superficial palisade that surrounds the colourless central region. In some Abolboda the mesophyll usually lacks distinct adaxial palisade (except in A. ciliata, A. grandis, and some A. macrostachya), and it is compact, mostly unlobed with some having air canals, in A. linearifolia these alternating pectinately with vascular bundles. In Orectanthe the mesophyll is of lobed, elongate cells and air canals are lacking.

Since Xyris is by far the largest genus and has the broadest geographic range and spread of habitat, it is not suprising that its foliar anatomy is the most diverse, particularly as to number and arrangement of foliar venation and vascular bundles. Veins range from few (1)-many, from 1 series with alternate bundles oriented in opposite directions to 2 or more series with bundles all similarly oriented; bundles may be compound or simple. Such variation ranges across what are thought to be sections. Achlyphila, nearestXyris in leaf character, still may be distinguished by its complete bundle sheaths around bundles, vascu­lar tissues without protoxylem lacunae and meta­xylem having irregular series and lacking the 2 obvious wide vessels. Abolboda and Orectanthe rarely have the compound vascular bundles so frequent in many Xyris. Tracheids with broad annular-helical thickenings have been found in leaf tips of some Abolboda.

Calcium oxalate as small crystals has been reported in the leaf mesophyll (Solereder and Meyer 1929) and the leaf epidermal wall (Tomlinson 1969) in Xyris. Raphides are lacking. Tannin is reported, mostly restricted to the epi­dermis, sometimes found in all cells or scattered irregularly. Starch is found in the rhizomes or larger stems and commonly in ground paren­chyma of leaf bases, the grains reported as com­pound in Xyris, simple, large, ellipsoid, or irregularly rounded in Abolboda.

INFLORESCENCE. In all Xyridaceae but Achlyphila the inflorescence is a closed, chaffy-bracted, conelike spike or a head which in a few species is

464 Xyridaceae

sessile, but which in most is atop a variously elongate naked or bracteate (some Abolboda, Achlyphila) scape. The flowers are sessile or subsessile in axils of chaffy, loosely to tightly im­bricate, spirally or decussately arranged bracts. In Achlyphila, however, the inflorescence is open, with flowers pedicellate in axils ofleaflike spathes.

The morphology of inflorescence bracts of spikes and heads is typically comparable to the sheaths of the foliage leaves. Outer and lower (sterile) ones may be strongly bladed or leaflike, as in involucrate Xyris (i.e., X. involucrata, X. mertensiana, X. nigricans, X. pallidula), or in the capitate Aratitiyopea gradate to surrounding foli­age leaves. In most the bracts are chaffy, some medially longitudinally herbaceous, but all typi­cally with broad, chaffy, or even scarious borders and most lacking blades, and in most the bracts are navicular to relatively broad, convex or keeled, or lingulate, the outer !-several ones sterile, mostly keeled, shorter, equal to, or longer than the fertile, grading into them. Costae (nerves) range from a single strong median one, or this bordered by few to several, generally less distinct laterals; in most the median zone is thickest and is sometimes evidently herbaceous. In Xyris this herbaceous zone, mostly sharply differentiated in texture and color, running the length of the bract or more often terminal or subterminal is referred to as dorsal area, and it may be specific in character. Bract arrangement may be entirely spiral, entirely distichous, or decussate at one level (usually proximally) and spiral upspike.

FLORAL STRUCTURE (Fig. 115). In all the genera the flowers are perfect and the perianth is in 2 differentiated whorls. The calyx is regular or nearly so in Achlyphila, Aratitiyopea, and Orectanthe, the 3 members distinct, chaffy, nav­icular or conduplicate; in Xyris and Abolboda it is distinctly irregular, in the former with the inner (anterior) sepal membranous and caducous, inclosing the rest of the flower in bud, the other 2 (outer) chaffy, navicular, keeled-carinate, free or connate, clasping the ripening fruit. In Abolboda the anterior sepal is generally reduced, even lack­ing, the laterals distinct, mostly navicular and carinate-keeled, often similar to spike bracts. In the other genera the sepals are strongly convex except towards the apex, there often with pro­nounced but entire keel.

The corolla is distinctive in all genera and is always tripartite. In Achlyphila petals are equal and distinct, with blades yellowish, tapering to base; in most Xyris the petals are equal, rarely

Fig. llSA-E. Xyridaceae. Flower structure in Xyris. A Ventral and cross-sectional view of sepals in bud. B Same of petals. C Staminode, showing yokelike blade and moniliform staminodial beard hairs. D Pistil, showing style base, tubular style branches, and stigmas. E Diagrammatic representation of flower. 1 Disarticulated dorsal sepal; 2 lateral sepals; 3 petal blades (claws foreshortened) with adnate stamens; 4 stamino­dia, claws foreshortened, showing flattened, bifurcate blades and terminal tufts of trichomes; 5 cross-section of flower towards base as oriented in bud; 6 stylar apex, showing horseshoelike stigma pattern at about level of staminode tip. (Krall988)

connate at base, more often with broad blades and clawed bases, and are mostly buttercup yellow, less often white. In Aratitiyopea the petals are equal, connate, the corolla tubular-salverform, white to pale purple. In Abolboda, they are equal, connate, funnelform-tubular to spreading, broad, white to blue or lavender lobes, while in Orectanthe the irregular gamopetalous yellowish (rarely lavender) corolla is distinctly bilabiate.

Fertile stamens are 3 in all genera (with the exception of one Xyris, which has 6) and are oppositipetalous. In Achlyphila they are hypogy­nous, and in the other four genera borne upon the petals with short or long filaments. In all genera the anthers are tetrasporangiate, dithecal, are mostly emarginate apically, the bases often separated by wide thin connective and auriculate to sagittate; they seem to be basifixed throughout.

Xyridaceae 465

Staminodia are lacking in Achyphila, Arati­tiyopea, and Orectanthe; in Abolboda they are lacking or filamentous and often less than 3, in any case borne upon the petals below corolla sinuses; in Xyris they are the most elaborate and are usu­ally hypogynous and long-clawed, the flat narrow claws branching distally, the flattened branches equipped with variably elongate, mostly penicil­late hairs or in a few cases reduced, rarely lacking.

In all genera the gynoecium is tricarpellate, the ovary superior. In Xyris, placentation ranges from entirely axile to basal-axile, basal, parietal, or marginal; in the other genera it is axile. In those Xyris with basal or basal-central placentation, the funiculus is often much longer than the mature seed. Styles are terminal, elongate in all genera. In Xyris the tubular style has 3 well-defined branches distally, each branch tubular-conduplicate and terminating in a U-shaped to shallowly infundi­bular, papillate to fimbriate stigmatic zone; in Achlyphila the stigmatic zone is nearly continuous with the style, small and 3-lobed; in Aratitiyopea the stylar apex is produced into 3 connivent, bristly glandular lobes; in Abolboda it is mostly infundibular with erose to fimbriate edges; in Orectanthe it is typically distinctly bent with a capitate-patelliform, papillate to fimbriate stigma. Stylar appendages are lacking in Achlyphila and Xyris, but well developed in the other three genera and always 3 in number. In all these cases there are 3 appendages on a style. In Abolboda the (usually) triquetrous style has a lateral, ascending to spreading or reflexed, stipitate or dilated­bladed appendage on each of the broader side wings and a 3rd, usually filamentous and reflexed, from the adaxial, narrower wing; the broader appendage blades are often auriculate at junction with stipe. In Aratitiyopea, the appendages are at the very style base, with erect, terete stipes and flattened, sharply reflexed, flabelliform blades. In Orectanthe, there is a similar basal arrangement, the narrow, firm, terete appendages erect around the style base, then sharply reflexed­curved.

EMBRYOLOGY. There is considerable vanat10n with respect to embryological traits within the family. Different kinds of endothecium and tape­tum structure have been reported, but the division of pollen mother cells is always successive. Mature pollen grains are indicated as 2- or 3-nucleate. The ovules are anatropous (Achlyphila and Alboboda), atropous (Xyris), or slightly campylotropous (Orectanthe), bitegmic and slightly crassinucellar (Tiemann 1985), and both Nuclear and Helobial

endosperm development are known (Tiemann 1985; Johri et al. 1992).

POLLEN MORPHOLOGY. Pollen grains sulcate (or occasionally disulcate?) in Xyris and inaperturate and spheroidal in Abolboda, Orectanthe, and probably Achlyphila (Fig. 116). They can be very large [most pollen grains of Abolboda studied by Erdtman (1952) and Carlquist (1960) have a diametre of over 100 [-Lm, those of the two species of Orectanthe range from 140-165 [,tm, but those of Achlyphila and Xyris have less than 50 [-Lm (Erdtman 1952)] and then only a small number of them is formed in each anther (Carlquist 1960). This enormous size of the pollen grains seems to be related to their function as reward for pollina­tors. The exine is thin and not very resistant to acetolysis; it is composed of 2 layers of different stainabilty and is underlain by a thin intine. The surface is smooth in Xyris and Achlyphila, but ornamented by large spines or knobs which are more resistant to acetolysis in the remaining three genera.

KARYOLOGY. Thus far, studies of microsporogen­esis in American Xyris have shown complements of n = 9 and root tip work showing 2n = 18. In African Xyris (X. capensis), however, sporophyte counts have been 2n = 34. Fedorov (1969) adds 2n

Fig. 116. Xyridaceae. Xyris involucrata, distal face of pollen with U-shaped sulcus, SEM X2200. (Photo Palynological Laboratory Stockholm)

466 Xyridaceae

= 26 and 32 for Xyris species. In Abolboda counts have been registered as n = 8, 9, 13, 17.

POLLINATION. No nectar is produced by the flow­ers of the Xyridaceae, and pollinating bees are at­tracted by pollen or imitated pollen masses (Vogel 1981); only Orectanthe is ornithophilous. S. Renner (pers. comm.) found Xyris sp. in Minas Gerais (Brazil) buzzed and pollinated by females of an anthophorid Exomalopsis sp.

FRUIT AND SEED. In all genera the fruit is a locu­licidal capsule. The 3 valves separate to the fruit base and the capsule walls are thickened or differ­entially thickened in most species except those of Xyris, where valves are usually thin.

Seeds in Achlyphila, Aratitiyopea, and Xyris are typically symmetric, ranging from subglobose to broadly ellipsoid or ovoid (in the former two), additionally (in Xyris) to variously ellipsoid or cylindric, frequently curved, often with the outer integument produced to an apical coma of scales or fimbriae. In Abolboda they are mostly thick­ened and curved dorsally, are asymmetrically obo­void, strongly ribbed on the thickened backs, whilst in Orectanthe they are laterally compressed, mitten-shaped, with a broad wing external to the embryo on one side, more narrowly on the edge opposite the thumb of the mitten. In Abolboda, Achlyphila, Aratitiyopea, and in most Xyris they are small, rarely over 1.2 mm. In some Xyris with basal or basal-central placentation some may ex­ceed 3 mm (including apiculus and apical coma) and in Orectanthe they may range from 2-4 mm. In all the embryo is basal or lateral, the endosperm copious, mealy, starchy and proteinaceous, the starch grains (in Abolboda) compound. Seed-coat sculpture in Xyris and Abolboda is often specifically distinct, being variously papillate, longitudinally distinctively ribbed, variously cross-ribbed, the outer integument variously produced in some Xyris into a distinctive coma of scales or hairs.

Both integuments take part in the composition of the seed coat, but only the tegmic layers, which are filled with a resinlike or tanninlike substance, provide mechanical strength (Carlquist 1960).

DISPERSAL. Seeds are shaken or fall from dehisc­ing capsules, particularly as aging bracts and sepals spread away from the fruit or as old scapes topple. These seeds are often buoyant, thus are left in drifts on the surface or are mixed with small sand particles and silt or homogenized peat in a shallow patina. If the substrate is moist, germina-

tion can take place within 2 weeks (in Xyris) and young seedlings can form a veritable turf on open seepage wherever there are clearings. On the other hand, since abundant moisture triggers germina­tion, if conditions are dry, Xyris seeds can remain dormant for indefinite periods. I have kept dry seed without refrigeration for up to 10 years and still had good germination in greenhouse fiats. I have run no such tests on seeds of the other genera.

PHYTOCHEMISTRY. Apart from common flavonol and flavone glycosides and proanthocyanidin, the anthraquinone chrysazin has been detected in a Xyris; this substance class may be widespread in Xyris as judged from the reddish sublimation on herbarium sheets. Cyanogenesis was found in one Xyris (Hegnauer 1963, 1986). The family was posi­tive in Harris and Hartley's (1980) tests for cell wall-bound ferulate.

RELATIONSHIPS WITHIN THE FAMILY. Only the Guayana Highlands has examples of all the genera, thus this ancient Precambrian land mass acts as what must be a primary centre. Circumstantial (morphologic) evidence points to 2 distinct clus­ters of character states, 1 having Abolboda, Aratitiyopea, and Orectanthe, the other contain­ing Achlyphila and Xyris. The former group is dis­tinguished by its polystichous, bifacial leaves in which there is no abrupt transition from sheath to blade, blades usually with a colorless hypodermis adaxially and often abaxially, a high degree of petal connation, spinose pollen, staminodia reduced to filaments or lacking, styles in most species asymmetric and appendaged, and placen­tation exclusively axile. The latter group has obvi­ously or obscurely distichous, equitant-sheathed, often ligulate, unifacially bladed leaves in which there is often an abrupt transition from sheath to blade, and blades typically lacking the colorless hypodermis, a low degree of petal connation or none, with pollen lacking spines, staminodia typi­cally present and bifid (lacking in the monotypic Achlyphila), styles symmetric and unappendaged, and placentation ranging from axile to basal, cen­tral, parietal, or marginal. Such evidence could lead to the suggestion that the 2 branches arose from ancestral stock, presumably in the Guayana Highlands, that was rhizomatous, perennial, with polystichous, bifacial leaves, was scapose, had flowers in bracteate racemes, had sepals and petals distinct and equal, had 6 distinct, hypogynous stamens and a superior tricarpellate ovary with an axile placentation (Kral 1992).

Xyridaceae 467

FAMILY AFFINITIES. Nakai (1943) was of the opinion that Abolboda and Orectanthe (first de­scribed as an Abolboda), on a basis of their dis­tinctive leaf and stem anatomy, and distinctive spinose pollen should be broken out of the Xyridaceae as the Abolbodaceae; this lead was followed temporarily by Takhtajan (1959), but only prior to the discovery of Achlyphila. Most phylogenists since (Takhtajan 1980; Cronquist 1981; Thorne 1967) treat all genera as Xyridaceae. The family has now often been considered as being most closely related to the Rapateaceae and Eriocaulaceae in the Commelinales. By and large this is confirmed by the recent cladistic and mo­lecular analyses of Linder and Kellogg (1995), who, however, additionally have brought the Bromeliaceae into the play, while in the restriction site analysis of Davis (1995), Xyris appears as sister to Carex.

DISTRIBUTION AND HABITATS. The family is es­sentially pantropic, with four of the five genera confined to S America and of these three, Achlyphila, Aratitiyopea, and Orectanthe are lim­ited to northern S America along with most of the 20 Abolboda species, with only a few of those reaching southward into S Brazil and only one ranging to Paraguay. Only Xyris has representa­tives in the Eastern as well as the Western Hemi­sphere with extensions northward into temperate America and eastern Asia (China, Taiwan). Nearly all species are heliophytic and inhabit acidic, moist to wet habitats (Fig. 117); however, a few are true aquatics (i.e., X. aquatica).

KEY TO THE GENERA

1. Petals gamopetalous; leaves polystichous; styles or ovary summit appendaged; pollen spinose or papillate; corolla regular or irregular; sepals 2- 3 2

- Petals usually distinct; leaves distichous, mostly equitant; styles unappendaged; pollen lacking spines or other protu­berances; corolla regular; sepals 3 4

2. Stylar appendages mostly well above style base on style; style often triquetrous at base; capsule apex thickened; flowers 1- several, the inflorescence sessile or on variously elongate, opposite-bracted scapes or in panicles; sepals 2(- 3) 3. Abolboda

- Stylar appendages at or around style base; style terete; cap­sule apex not appreciably thickened; flowers many in dense, globose or hemispheric large heads; sepals 3 3

3. Corollas arching-spreading, irregular, yellow (rarely redpurple); style apex bent outward, stigma capitate, lateral-terminal, papillate; seeds winged, 2-4mm, irregular, mitten-shaped 5. Orectanthe

- Corollas erect, regular, salverform, white to purple; stigma terminal on erect style tip, trilobed, the lobes pilose; seeds wingless, ridged-and-pitted, symmetric 4. Aratitiyopea

Fig. 117. Xyridaceae. Orectanthe sceptrum, growing on flooded peat together with Xyris sp. and Eriocaulaceae. Venezuela, Mt Roraima. (Photo K. Kubitzki)

4. Flowers distinctly pedicelled; sepals alike; staminodia lack­ing; style unbranched, the stigma trilobed, capitate; petals lacking claws; stamens hypogynous I. Achlyphila

- Flowers subsessile or sessile; sepals unlike, the lateral ones chaffy and keeled, the inner one membranous; staminodia usually present, mostly bibrachiate; style 3-branched, the stigmas mostly U-shaped; petal blades on claws; stamens borne on petals 2. Xyris

GENERA OF THE XYRIDACEAE

1. Achlyphila Maguire & Wurdack

Achlyphila Maguire & Wurdack, Mem. N.Y. Bot. Gard. 10 (2): 12 (1960); Kral, Ann. Mo. Bot. Gard. 79: 874-877 (1992), rev.

Perennial from slender, branched rhizomes; leaves narrowly ascending, equitant-distichous, the blades linear-triangular, unifacial. Scapes single, terminal, compressed; inflorescence usu­ally with 2 approximate, distichously arranged

468 Xyridaceae

leaflike spathes subtending 1-3 flattened­pedicelled flowers, sepals 3, landform, chaffy; pet­als 3, distinct, unclawed, dull yellow; stamens 3, distinct from petals; staminodia lacking; style erect, linear, unappendaged. Only one sp., A. disticha Maguire & Wurdack, summit elevations on Cerro Neblina along the Brazil-SW Venezuela border (1800-2300 m).

2. Xyris L.

Xyris L., Sp. Pl.: 42 (1753); Smith & Downs in Fl. Brasilica 9 (2): 1-215 (1968); Kral, Sida 2: 177-260 (1966), spp. USA & Canada; Kral, Ann. Mo. Bot. Gard, 75: 522-722 (1988), spp. northern S America.

Usually perennials, or annual to short-lived plants; usually rosulate (less often caulescent), solitary or caespitose, sometimes rhizomatous or bulbous herbs; axis sympodial; leaves mostly equitant and distichous. Scapes naked, terete to compressed, ending in a single conelike spike or a head (rarely bispicate); outer bracts sometimes involucra! but mostly chaffy, grading to 1 or more fertile bracts; flowers subsessile, solitary in bract axils; sepals 3, the 2 laterals mostly chaffy, the inner membranous and infolding the corolla bud, abcissing when flower spreads; petals 3, distinct, mostly clawed, yellow( -white); stamens 3; staminodia hypogynous, mostly long-clawed, bibrachiate, rarely reduced or lacking; style erect, unappendaged, conduplicate-tubular, 3-branched, terminating in U-shaped or semi­infundibular stigmas. n = 9, less often 17; 2n = 18, rarely 34. Nearly 300 described spp., mostly in S America, several in Africa, Australia, and Asia, in America extending N to Canada and in Asia north to China and Taiwan. Three sections have been described, mostly based on differences in placen­tation, but their distinction is risky at best, par­ticularly if there is no geographic correlation as was once believed; a study of Xyris of the Guayana Highlands reveals examples of all three "sections" from the same habitat in the savannas and tepuis of that region.

3. Abolboda Kunth Fig. 114

Abolboda Kunth in Humb. & Bonpl., Pl. Aequinoct. 2: 25, pl. 114 (1809); Kral, Ann. Mo. Bot. Gard. 79: 820-874 (1992), rev.

Cespitose or solitary, mostly glabrous perennials, rarely annuals; leaves mostly basal. Inflorescences subsessile to strongly scapose, scapes naked or

bracteate, terminating in a head or spike (rarely in a panicle of spikes), the inflorescence bracts mostly chaffy in spiral, the lower empty, the fertile loosely or tightly imbricate, each subtending a single flower; sepals 2( -3); corolla gamopetalous, actinomorphic, salverform, white, blue or laven­der; stamens 3; staminodia 0-1-3; style usually appendaged, mostly triquetrous-winged. Twenty neotropical spp., boggy, warm to cool habitats, centring in the savannas of northern S America.

4. Aratitiyopea Steyerm. & Berry

Aratitiyopea Steyerm. & Berry, Ann. Mo. Bot. Gard. 71: 297 (1984); Kral, Ann. Mo. Bot. Gard. 79: 877-879 (1992), rev.

Robust, "Navia" -like perennials from a thick rhi­zome; leaves polystichous, crowded toward shoot apex, linear-lorate, lingulate, sharp-tipped, the longest downstem, the upper grading into a large, chaffy-involucrate, hemispheric head of many bracts, the inner ones increasingly narrower and directly subtending flowers; sepals 3, similar to cephalar bracts but slightly longer; corolla tubular-salverform, actinomorphic, 7-10 em, white to pale purple; stamens 3; staminodia lack­ing; ovary dorsiventrally compressed; style straight, basally provided with stipitate, recurved, broadly flabellate appendages. Only one sp., A.· lopezii (L.B. Smith) Steyerm. & Berry, with two varieties, rare on arenaceous rock outcrops in NW Brazil, SW Venezuela, and SE Colombia, at 250-1600 m. Highly ornamental, described earlier as the bivarietal Navia lopezii by L.B. Smith (Bot. Mus. Leafl. 15: 40. 1951; ibid 16: 195. 1954).

5. Orectanthe Maguire Fig. 117

Orectanthe Maguire, Mem. N.Y. Bot. Gard. 10:2-3. 1958; Kral, Ann. Mo. Bot. Gard. 79: 879-885 (1992), rev.

Glabrous perennials; stems either short, stout, producing dense basal rosettes or lax, decumbent, branching to short, erect tips. Leaves polysti­chous, clasping-based, sharp-tipped; scapes 1-several, naked, variously elongate. Inflorescence a large, terminal burrlike head; outer and cephalar bracts shorter than sepals; sepals 3, chaffy; corolla gamopetalous, bilabiate, pale yellow, rarely pur­plish; stamens 3; staminodia lacking; placentation axile; style appendages basal, linear, doubled back. Two spp., northern S America on the Roraima sandstones of the Guayana Highland at medium to high elevations, usually in boggy pockets amongst rocks and in full sun.

Xyridaceae 469

Selected Bibliography

Arber, A. 1922. Leaves of the Farinosae. Bot. Gaz. 74: 80-94. Carlquist, S. 1960. Anatomy of Guayana Xyridaceae: Abol­

boda, Orectanthe, and Achlyphila. Mem. N.Y. Bot. Gard. 10 (2): 65-117.

Cook, C.D.K., Gut, B.J., Rix, E.M., Schneller, J., Seitz, M. 1974. Water plants of the world. The Hague: Junk.

Cronquist, A. 1981. See general references. Davis, J .I. 1995. A phylogenetic structure for the monocotyle­

dons, as inferred from chloroplast DNA restriction site variation, and a comparison of measures of clade support. Syst. Bot. 20: 503-527.

Engler, A. 1887. Xyridaceae. In: Engler, A., Prantl, K. (eds.) Natiirliche Pfianzenfamilien II. 4: 18-20. Leipzig: W. Engelmann.

Erdtman, G. 1952. See general references. Fedorov, An. A. 1969. See general references. Frolich, D., Barthlott W. 1988. See general references. Hamann, U. 1961. Merkmalsbestand und Verwandtschafts-

beziehungen der Farinosae. Ein Beitrag zum System der Monocotyledonen. Willdenowia 2: 639-768.

Hamann, U. 1962. Weiteres tiber Merkmalsbestand und Verwandtschaftsbeziehungen der "Farinosae." Ibid. 3: 169-297.

Harris, P.J., Hartley, R.D. 1980. See general references. Hegnauer, R. 1963, 1986. See general references. Idrobo, J.M. 1954. Xiridaceas de Colombia. Caldasia 6 (20):

184-260. Johri, B.M. eta!. 1992. See general references. Kral, R. 1966. Xyris (Xyridaceae) of the continental United

States and Canada. Sida 2: 177-260. Kral, R. 1983. The Xyridaceae in the southeastern United

States. J. Arnold Arbor. 64: 421-429. Kral, R. 1988. The genus Xyris (Xyridaceae) in Venezuela and

contiguous northern South America. Ann. Mo. Bot. Gard. 75: 522-722.

Kral, R. 1992. A treatment of American Xyridaceae exclusive of Xyris. Ann. Mo. Bot. Gard. 79: 819-885.

Linder, H.P., Kellogg, E.A. 1995. Phylogenetic patterns in the Commelinid clade. In: Rudall, P.J., Cribb, P.J., Cutler, D.F., Humphries, C.J. (eds.) Monocotyledons: systematics and evolution, Vol. 2. London: Royal Botanic Gardens, Kew, pp. 473-496.

Maguire, B. 1958. Xyridaceae. In: Maguire, B., Wurdack, J.J., eta!. (eds.) Botany of the Guayana Highland, part III. Mem. N.Y. Bot. Gard. 10 (1): 1-19. [Orectanthe described]

Maguire, B., Wurdack, J.J. 1960. Xyridaceae. In: Maguire, B., Wurdack, J.J., eta!. (eds.) Botany of the Guayana Highland, part IV. Mem. N.Y. Bot. Gard. 10 (2): 11-15. [Achlyphila described.]

Malme, G.O.A. 1930. Xyridaceae. In: Engler, A., Prantl, K. (eds.) Natiirliche Pfianzenfamilien, 2nd edn., 15a: 35-38, figs 11-15. Leipzig: W. Engelmann.

Nakai, T. 1943. Ordines, familiae, tribi, genera, sectiones, spe­cies, varietates, formae et combinationes novae a Prof. Nakai-Takenoshin adhuc et navis edita. Tokyo.

Solereder, H., Meyer, F.J. 1929. Xyridaceae. Systematische Anatomie der Monokotyledonen 4. Berlin: Borntraeger, pp. 36-50.

Suessenguth, K., Beyerle, R. 1935. Dber die Xyridaceengattung Abolboda Humb. et Bonpl. Bot. Jahrb. Syst. 67: 132-142.

Takhtajan, A. 1959. Die Evolution der Angiospermen. Jena: G. Fischer.

Takhtajan, A. 1980. Outline of the classification of flowering plants (Magnoliophyta). Bot. Rev. 46: 225-359.

Thorne, R.F. 1967. A phylogenetic classification of the Angio­spermae. Evol. Bioi. 9: 35-106.

Tiemann, A. 1985. Untersuchungen zur Embryologie, Bliiten­morphologie und Systematik der Rapateaceen und der Xyridaceen-Gattung Abolboda (Monocotyledoneae). Diss. Bot. 82: 1-202. Lehre, Cramer.

Tomlinson, P.B. 1969. Commelinales-Zingiberales. In: Metcalfe, C.R. (ed.) Anatomy of monocotyledons, Vol. 3. Oxford: Clarendon Press.

Vogel, S. 1981. Bestaubungskonzepte der Monokotylen und ihr Ausdruck im System. Ber. Dtsch. Bot. Ges. 94: 663-673.