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


This taxon is accepted by eMonocot

General Description

Annual or perennial herbs, often in seasonally or permanently wet sites; stems upright, base sometimes swollen in perennial species. Leaves alternate, simple, linear, distichous, few to numerous, basal sheath open, blade flattened to terete. Inflorescence a condensed pedunculate spike; flowers in the axils of densely crowded often coriaceous bracts, forming a spherical, ovoid or elongate head (the spike). Flowers 3-merous, bisexual; calyx-lobes 3, the adaxial at first forming a hood-like structure over the bud, the laterals smaller; corolla tubular, divided above into 3 broad spreading usually yellow but sometimes white, blue or orange petals. Stamens 3, opposite the petals, often with 3 staminodes alternating with them. Ovary (1–)3-locular, with numerous ovules and axile or parietal placentation; style 1, sometimes divided into 3 at the apex. Fruit a loculicidal or irregularly dehiscent capsule. Seeds numerous, small, with endosperm.

Notes: A medium-sized family of mostly small annual or perennial herbs. In South America the inflorescences of a few species are collected and sold as dried flowers; otherwise the only economic importance of the family is as weeds of wet places, particularly rice fields.

Perennial or annual herbs. Leaves mostly radical, tufted, linear, terete or filiform, sheathing at the base. Flowers hermaphrodite, slightly zygomorphic, arranged in pedunculate terminal globose or cylindrical heads; bracts imbricate, leathery or rigid, the lower sometimes forming an involucre. Sepals 3 or rarely 2, the lateral 2 exterior, boat-shaped, keeled, glumaceous, the third interior, membranous, forming a hood over the corolla and pushed aside as the latter develops. Corolla with a short or long tube and 3 equal spreading lobes. Stamens 3, opposite the corolla-lobes, and 3 alternate staminodes or the latter absent; anthers 2-locular, opening by slits. Ovary superior, 1-locular, with 3 parietal placentas or imperfectly 3-locular at the base; style simple or 3-lobed. Ovules numerous to few. Fruit a capsule enclosed in the persistent, corolla-tube. Seeds numerous, with copious endosperm and small embryo.

Plantas herbáceas, perenes ou raramente anuais, terrestres, frequentemente helófitas, raramente aquáticas; caule rizomatoso, em geral com entrenós curtos. Folhas rosuladas ou distribuídas ao longo do caule, polísticas ou dísticas; bainha aberta, algumas vezes com lígula marginal na transição da bainha para a lâmina (Xyris e Achlyphila); lâmina isobilateral (Xyris e Achlyphila) ou bifacial, achatada, elíptica, cilíndrica ou filiforme. Inflorescência lateral ou terminal, em geral espiga no ápice de um escapo áfilo (Xyris) ou bracteado (Abolboda e Orectanthe) portando brácteas imbricadas ou inflorescêcia ramificada e pedunculada (Achlyphila) ou mais raramente séssil (Aratitiyopea). Flores 3-meras, heteroclamídeas; sépalas geralmente três, dimórficas (Xyris, Abolboda e Orectanthe), sendo a abaxial ou anterior diferente das duas adaxias (laterais) ou raramente a sépala adaxial suprimida (Abolboda); pétalas amarelas, azuis, púrpuras ou brancas, concrescidas entre si ou livres; estames epipétalos (exceto Achlyphila); anteras tetrasporangiadas, deiscência longitudinal, latrorsa ou introrsa; grão de pólen elipsoide e sulcado ou esferoidal e inaperturado; ovário 1 ou 3-locular pelo menos na base; placentação basal, supra-basal, central-livre ou parietal, óvulos anátropos, campilótropos ou ortótropos; glândula dorsal desenvolvida e pedicelada no ápice do ovário (Aratitiyopea e Orectanthe), ou delicada, desigual ao longo do estilete (maioria das Abolboda), ausente em Xyris; estilete simples, em geral 3-ramificado na região apical, estigma plumoso (exceto Achlyphila). Fruto cápsula loculicida; sementes geralmente numerosas, pequenas.

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, 1many, 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 1locular 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 V-shaped stigmas, or variously dilated to infundibular or laminar or subcapitate, usually papillate or fringed stigmatic zones. Fruit capsular, mostly loculicidal; seeds usually numerous, rarely 1, mostly with strong longitudinal ridges and finer cross-lines, translu cent or farinose-opaque, the embryo small, situ ated 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.

Ecology

Nearly all species are heliophytic and inhabit acidic, moist to wet habitats; however a few are true aquatics (i.e. X. aquatica).

Distribution

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).

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.

  Bibliography

 Information From

eMonocot
http://e-monocot.org
eMonocot. (2010, 1st November). Retrieved Wednesday, 8th February, 2012, from http://e-monocot.org.
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Flora of Tropical East Africa (FTEA)
http://kew.org/efloras/
Royal Botanic Gardens, Kew, 2004. eFloras: Iridaceae. [online] Available at: http://kew.org/efloras/ [Accessed 2013-08-02]
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Flora of West Tropical Aftrica (FWTA)
http://kew.org/efloras/
Royal Botanic Gardens, Kew, 2004. eFloras: Iridaceae. [online] Available at: http://kew.org/efloras/ [Accessed 2013-08-02]
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Xyridaceae
http://xyridaceae.e-monocot.org
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World Checklist of Selected Plant Families
http://apps.kew.org/wcsp/
WCSP 2014. 'World Checklist of Selected Plant Families. Facilitated by the Royal Botanic Gardens, Kew. Published on the Internet; http://apps.kew.org/wcsp/ Retrieved 2011 onwards
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