Xyridaceae C.Agardh

Xyridaceae, F.N. Hepper. Flora of West Tropical Africa 3:1. 1968

Morphology General Habit

Perennial or annual herbs

Morphology Leaves

Leaves mostly radical, tufted, linear, terete or filiform, sheathing at the base

Morphology Reproductive morphology Flowers

Flowers hermaphrodite, slightly zygomorphic, arranged in pedunculate terminal globose or cylindrical heads; bracts imbricate, leathery or rigid, the lower sometimes forming an involucre

Morphology Reproductive morphology Flowers Calyx

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

Morphology Reproductive morphology Flowers Corolla

Corolla with a short or long tube and 3 equal spreading lobes

Morphology Reproductive morphology Flowers Androecium

Stamens 3, opposite the corolla-lobes, and 3 alternate staminodes or the latter absent; anthers 2-locular, opening by slits

Morphology Reproductive morphology Flowers Gynoecium

Ovules numerous to few Ovary superior, 1-locular, with 3 parietal placentas or imperfectly 3-locular at the base; style simple or 3-lobed

Morphology Reproductive morphology Fruits

Fruit a capsule enclosed in the persistent, corolla-tube

Morphology Reproductive morphology Seeds

Seeds numerous, with copious endosperm and small embryo

Milliken, W., Klitgard, B. and Baracat, A. (2009 onwards), Neotropikey - Interactive key and information resources for flowering plants of the Neotropics. http://creativecommons.org/licenses/by/3.0

Morphology General Habit

Herbs, perennial, or rarely annual; terrestrial, helophytic, rarely aquatic; caudex usually short

Morphology Leaves

Leaves usually with short internodes, ranked or polystichous; sheath open, broad or not well developed, often equitant and keeled, with or without a marginal ligule at  apex (Xyris L. and Achlyphila Maguire & Wurdack); blade isobilateral (Xyris and Achlyphila), or bifacial, ensiform or terete (sometimes filiform, less than 1 mm)

Morphology Reproductive morphology Inflorescences

Inflorescence usually an imbricate -bracted spike, narrow to sometimes broad, rarely reduced to 1 or 2 flowers, rarely racemose (Aratitiyopea Steyerm. & P. Berry), rarely compound; lateral or terminal; mostly long-pedunculate, peduncles bounded by a conspicuous or inconspicuous open, basal sheath, infrequently with pair(s) of subopposite bracts along axis (Abolboda Humb. & Bonpl.); inflorescence subtended by one or more bracts, rarely involucrate

Morphology Reproductive morphology Flowers

Flowers rarely pedicellate; subtended by a bract, bract usually indurate or coriaceous; hermaphrodite, 3- merous (except for  calyx in some Abolboda); perianth in 2 differentiated whorls; sepals dimorphic, abaxial sepal rarely absent or weakly developed (Abolboda), mostly caducous at anthesis (Abolboda and Xyris), usually membranous, connivent or basally connate; adaxial sepals chaffy to indurate, navicular and keeled (except Achlyphila), petals equal or subequal, free and usually clawed or fused and tubular, salverform, or porrect; yellow, blue, lavender, purple, or white; staminodia distally bifurcate, distally with moniliform hairs, hairs usually copious, branches adhering to the adjacent corolla lobes (Xyris), or staminodia filamentous (some Abolboda spp.); stamens epipetalous (except Achlyphila); anthers tetrasporangiate, dehiscing longitudinally, dehiscence latrorse or introrse; pollen ellipsoid and sulcate (Xyris), or spherical and lacking an obvious aperture; ovary 1- or 3-locular, at least basally, placentation basal, free -central or parietal often on intruded placentae; dorsal gland large and stalked, on  ovary apex (Aratitiyopea and Orectanthe Maguire), or delicate, unequal, and along  style (most Abolboda); style 3-branched into stylodia or stigmatic branches (except some Xyris and Achlyphila), stigma plumose (except Achlyphila)

Morphology Reproductive morphology Fruits

Fruita loculicidal capsule; seeds usually numerous, ellipsoid to spherical, longitudinally striate to ridged, with finer cross reticulations or ridges.

Note

Notes on delimitation: Xyridaceae are generally considered closely related to Eriocaulaceae, and are presently included in the broadly defined order Poales, part of the large commelinid clade. Two lineages are present in Xyridaceae, which have been recognized at the sub - or familial level. The most recent phylogenetic studies resolve the family as monophyletic, albeit generic sampling is not yet complete. Xyridaceae flower during periods of high precipitation and individual flowers of most species last only a few hours. Most species occur in oligotrophic, often acidic, boggy or savanna habitats. Xyridaceae are important components of environmentally sensitive habitats. Xyridaceae have limited, mostly local economic use. In South America some Xyridaceae infructescences are harvested as dried flowers, thus depleting the seed bank. A few Xyris species are cultivated ornamentals, some as aquaria plants. Leaves from relatively robust species of Xyris are woven into mats or objects. Mucilage from Xyris species has been used topically for skin aliments, and some species exhibit antimicrobial activity. A cathartic compound has been isolated from the leaves and stems of a Xyris species. Leaves of Orectanthe are a reported headache remedy. Number of genera: Abolboda Humb. & Bonpl. (23 spp.) Achlyphila Maguire & Wurdack (1 sp.) Aratitiyopea Steyerm. & P. E. Berry (1 sp.) Orectanthe Maguire (2 spp.) Xyris  L. (ca. 390 spp.)

Distribution

Plants of seasonally or permanently wet habitats. Native. All genera except for Xyris are endemic to the Neotropics, and many species are narrowly endemic.

Diagnostic

Distinguishing characters (always present): Leaves alternate, simple. Flowers bisexual. Perianth dichlamydeous. Sepals dimorphic (sometimes weakly so). Corolla and androecium 3-merous. Gynoecium trimerous; ovarysuperior. Seed coat variously ridged. Fruit a dehiscentcapsule. Plants mostly with a short caudex. Inflorescence usually long-pedunculate. Petal midvein conspicuous (Abolboda, Aratitiyopea and Orectanthe). Outer androecial whorl present and sterile (never in Achlyphila, Aratitiyopea, and Orectanthe). Anthers sagittate. Staminodia conspicuous in Xyris; usually branched, and with copious moniliform hairs. Style branched into three stylodia or stigmas (except Achlyphila); stigmas plumose (except Achlyphila). Gynoecium appendages sometimes present (never in Achlyphila and Xyris). The genera of Xyridaceae are morphologically quite distinct from each other. Xyris species and Achlyphila are yellow-flowered and have equitant or terete leaves. Xyris have elaborate staminodia. A few Abolboda species, Aratitiyopea, and Orectanthe are relatively robust. Aratitiyopea is markedly a mesophyte. Orectanthe spp. differ from robust Abolboda in having a naked peduncle, yellow flowers, and gynoecium glands located on top of the ovary. Abolboda have bifacial leaves, often subopposite peduncular bracts, blue to purple or white corollas, sometimes filamentous staminoida, and usually small appendages on the style. Genera of Xyridaceae are readily distinguished by suites of morphological characters, including overall plant size.  Abolboda exhibits the most variability in the distinguishing characters. Plants are rosulate (except A. linearifolia Maguire) with bifacial and polystichous (except A. spruceana Malme) leaves. The inflorescence is a long-pedunculate spike with indurate bracts and sepals, occasionally epedunculate and reduced to a single (-few) flower. Many species have one or more subopposite pairs of bracts along the peduncle. Achlyphila is rhizomatous with an erect leaf-bearing axis. The leaves are equitant and ensiform. The inflorescence is compound, bracteate, with long-pedicellate flowers. The corolla is yellow and apopetalous. The stamens are hypogenous. Achlyphila is known only from Co. de la Neblina on the Venezuelan/Brazilian frontier. Aratitiyopea is rhizomatous with a relatively long, decumbent stem. The species is mesophytic and has relatively wide bifacial leaves. The nearly sessileinflorescence is a compoundraceme with highly colored bracts. The corollas are long tubular and either white or bright magenta. There is a fleshygland in the dorsal position on top of the ovary. Orectanthesceptrum (Oliv.) Maguire has a distinctive agave-like rosette of wide, glaucous leaves; O. ptaritepuiana (Steyerm.) Maguire has an elongate stem, with wide glabrous leaves. The inflorescence is a long-pedunculate broad spike, with induratepersistent bracts and adaxial sepals. The corollas are yellow and porrect.  Almost all Xyris species have yellow epedicellate flowers in spikes. The staminodia are a conspicuous part of the floral display. The floral bracts have an abaxial patch. Pollen is ellipsoid (vs. spherical in the rest of the family). Key differences from similar families: Species of Xyridaceae and the following families are sometimes confused, particularly as dried, pressed specimens. They can be distinguished with these gross morphological characters: Eriocaulaceae have filamentous to multicellular, e- or glandular hairs of various configuration, that are grouped or paired on the roots. The peduncular bract in Eriocaulaceae is a closed sheath (few exceptions) and the inflorescence is involucrate. Flowers of Eriocaulaceae are highly reduced and modified; when available for examination, the family is easily confirmed. Many genera of Rapateaceae are vegetatively distinct from Xyridaceae in having a conspicuous leaf midvein and open, conduplicate leaf sheath. Flowers of Rapateaceae are subtended by numerous coriaceous bracts and have six fertile stamens dehiscing by distal pores. Leaf margins of Xyridaceae never bear spines as in many Bromeliaceae. Aratitiyopea is further distinguished by its flower length, large spherical pollen grains, and the presence of gynoecium appendages. Bracts of long-pedunculate Bromeliaceae exhibit spiraled phyllotaxis. Flowers of Bromeliaceae may have petal appendages, have six fertile stamens, septal nectaries, and may have an inferior ovary. Some species of Rhynchospora Vahl and Bulbostylus Kunth (Cyperaceae) have indurate or coriaceous bracts, and spicate inflorescences similar to some species of Xyris. The floral characters of the two families are very distinctive. The perianth of Cyperaceae is composed of glumes, and species with unisexual or bicarpellate flowers are easily distinguished from Xyridaceae. Cyperaceae are vegetatively distinct from Xyridaceae in having a closed leaf sheath.