Lisa M. Campbell*, Maria das Graças Lapa Wanderley** and Gisele de Oliveira Silva**
* New York Botanical Garden, NY, USA.** Instituto de Botânica de São Paulo, SP, Brazil.
Herbs, perennial, or rarely annual; terrestrial, helophytic, rarely aquatic; caudex usually short. 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). 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. 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). Fruit a loculicidal capsule; seeds usually numerous, ellipsoid to spherical, longitudinally striate to ridged, with finer cross reticulations or ridges.
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.
Distribution in the Neotropics
- Plants of seasonally or permanently wet habitats.
Distinguishing characters (always present)
- Leaves alternate, simple.
- Flowers bisexual.
- Perianth dichlamydeous.
- Sepals dimorphic (sometimes weakly so).
- Corolla and androecium 3-merous.
- Gynoecium trimerous; ovary superior.
- Seed coat variously ridged.
- Fruit a dehiscent capsule.
Other important characters
- 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).
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.
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.)
Useful tips for generic identification
- 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.
Notable genera and distinguishing features
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 sessile inflorescence is a compound raceme with highly colored bracts. The corollas are long tubular and either white or bright magenta. There is a fleshy gland in the dorsal position on top of the ovary.
- Orectanthe sceptrum (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 indurate persistent 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).
- Native. All genera except for Xyris are endemic to the Neotropics, and many species are narrowly endemic.
- 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.
Benko-Iseppon, A. M. and M. G. L. Wanderley. 2002. Cytogenetic studies on Brazilian Xyris species (Xyridaceae). J. Linn. Soc., Bot. 138: 245-252.
Campbell, L. M. 2004. Xyridaceae. Pp. 492-493. In: N. Smith et al., eds. Flowering Plants of the Neotropics. Princeton University Press.
Campbell, L. M. 2004. Anatomy and Systematics of Xyridaceae with Special Reference to Aratitiyopea. Dissertation. City University of New York.
Campbell, L. M. 2005. Contributions towards a monograph of Xyridaceae: A revised nomenclature for Abolboda (Xyridaceae). Harvard Papers in Botany 10: 137-146.
Campbell, L. M. and D. W. Stevenson. 2005. Vegetative anatomy of Aratitiyopea lopezii (Xyridaceae). Acta Bot.Venez. 28: 395-407.
Campbell, L. M. and D. Wm. Stevenson. 2007. Inflorescence architecture and floral morphology of Aratitiyopea lopezii (Xyridaceae). Aliso 23: 227-233.
Carlquist, S. 1960. Anatomy of Guayana Xyridaceae: Abolboda, Orectanthe, and Achlyphila. Mem. New York Bot. Gard. 10(2): 65-117.
Idrobo, J. M. 1954. Xiridaceas de Colombia. Caldasia 6: 185-260.
Kral, R. 1988. The genus Xyris (Xyridaceae) in Venezuela and contiguous northern South America. Ann. Missouri Bot. Gard. 75: 522-722.
Kral, R. 1992. A treatment of American Xyridaceae exclusive of Xyris. Ann. Missouri Bot. Gard. 79: 819-885.
Kral, R. 1998. Xyridaceae. Pp. 461-469. In: K. Kubitzki, ed. The Families and Genera of Vascular Plants. Vol. IV. Alismatanae and Commelinanae (Except Gramineae). Springer-Verlag, Berlin, Heidelberg, New York.
Kral, R. 1994. Xyridaceae. Pp. 3-90; 115-123. In: A. R. A. Görts-van-Rijn, ed. Flora of the Guianas. 15.
Kral, R. 1999. Xyridaceae. Pp. 15-36. In: G. Harling and B. Sparre, eds. Flora of Ecuador. No. 63. Univ. of Goteborg, Sweden.Kral, R. 2005. Xyridaceae. Pp. 526-575. In: J. A. Steyermark, P. E. Berry, K. Yatskievych, & B. K. Holst, eds. Flora of the Venezuelan Guayana. Vol. 9. Missouri Botanical Garden Press, St. Louis.
Kral, R. and M. G. L. Wanderley. 1988. Ten novelties in Xyris (Xyridaceae) from the Planalto of Brazil. Ann. Missouri Bot. Gard. 75: 352-372.
Kral, R. and M. G. L. Wanderley. 1995. Xyridaceae. Pp. 781-802. In: B. L. Stannard, ed. Flora of the Pico das Almas: Chapada Diamantina-Bahia, Brazil. Royal Botanic Gardens, Kew.
Kraus, J. E., M. G. Sajo, C. L. Dias-Leme, & M. G. L. Wanderley. 1994. Aspectos morphológicos do desenvolvimento pós-seminal em espécies de Xyris L. (Xyridaceae). Hoehnea 21(1/2): 29-38.
Sajo, M. G. and P. J. Rudall. 1999. Systematic vegetative anatomy and ensiform leaf development in Xyris (Xyridaceae). J. Linn. Soc., Bot. 130: 171-182.
Tiemann, A. 1985. Untersuchungen zur embryologie, blütenmorphologie und systematik der Rapateaceen und der Xyridaceen-gattung Abolboda (Monocotyledoneae). Diss. Bot. 82. J. Cramer, Vaduz.
Tomlinson, P. B. 1969. Anatomy of the Monocotyledons. Vol. III. Commelinales-Zingiberales. Claredon Press, Oxford.
Wanderley, M. G. L. 1989. Xyridaceae. Flora Estado Goiás. Vol. 11: 1-81.
Wanderley, M. G. L. 1992. Estudos Taxonômicos no Gênero Xyris L. (Xyridaceae) da Serra do Cipó, Minas Gerais, Brasil. Dissertation, Instituto de Biociências, São Paulo.
Wanderley, M. G. L. 2003. Xyridaceae. In: M. G. L. Wanderley, G. J. Shepherd, and A. M. Giulietti, coordinators. Flora fanerogamica do Estado de São Paulo. FAPESP: Editora Hucitec, Sao Paulo.
How to cite
Campbell, L.M., Wanderley, M.G.L. & Silva, G.O. (2009). Neotropical Xyridaceae. In: Milliken, W., Klitgård, B. & Baracat, A. (2009 onwards), Neotropikey - Interactive key and information resources for flowering plants of the Neotropics. http://www.kew.org/science/tropamerica/neotropikey/families/Xyridaceae.htm.
Click images to enlarge
Habit of Albolboda poarchon © Suzana Martins, Instituto de Botânica de São Paulo.
Flower of Albolboda poarchon © Suzana Martins, Instituto de Botânica de São Paulo.
Habit of Albolboda pulchella © W. Milliken, RBG, Kew.
Xyris bialata: A. habit; B. detail the region of transition between the sheath and leaf blade, with conspicuous ligule.; C. transversal section of blade, showing the vascular bundles uni- to multipolar; D. Scape two-winged with two sterile reducet bract; E. cylindric at spike; F. sterile bract; G. floral bract with apical macula, margins ciliate; H. flower; I. anterior sepal, showing carina extended and ciliatel; J. fruit; L. placentation central; M. seed. © Maria das Graças Lapa Wanderley and Maria Cecília Tomasi, Instituto de Botânica de São Paulo.
Flower of Xyris cipoensis © Suzana Martins, Instituto de Botânica de São Paulo.
Xyris cipoensis species: A. habit; B. apex of the leaf; C. spike; D. sterile bract; E. floral bract; F. flower, showing externally floral bract, lateral sepals and corolla; G. open flower, showing lateral sepal, corolla, androecium and gynoeceum; H. detail of the bifid staminodium; I. fruit showing placentation basal; J. detail of the seed © Maria das Graças Lapa Wanderley and Maria Cecília Tomasi, Instituto de Botânica de São Paulo.
Flower of Xyris hymenachne © Suzana Martins, Instituto de Botânica de São Paulo.
Xyris laxifolia: A. habit; B. spike; C-D. sterile bract; E. floral bract; F. flower showing gynoecium and androecium; G. lobe of the corolla with 1 stamen and 1 staminodium; H. open fruit showing parietal placentation; I. seed © Maria das Graças Lapa Wanderley and Maria Cecília Tomasi, Instituto de Botânica de São Paulo.
Flower of Xyris machrisiana © Suzana Martins, Instituto de Botânica de São Paulo.
Flowers of Xyris paradisiaca © Suzana Martins, Instituto de Botânica de São Paulo.
Base of plant of Xyris paradisiaca © Suzana Martins, Instituto de Botânica de São Paulo.
Base of the plant of Xyris phaeocephala © Maria das Graças Lapa Wanderley, Instituto de Botânica de São Paulo.
Habit of Xyris phaeocephala © Maria das Graças Lapa Wanderley, Instituto de Botânica de São Paulo.
Flower of Xyris spectabilis (pollination) © Suzana Martins, Instituto de Botânica de São Paulo.
Habit of Xyris teres © Suzana Martins, Instituto de Botânica de São Paulo.
Detail of the spike of Xyris teres © Suzana Martins, Instituto de Botânica de São Paulo.
Habit of Xyris tortula © Maria das Graças Lapa Wanderley, Instituto de Botânica de São Paulo.
Staminodium of Xyris tortula © Suzana Martins, Instituto de Botânica de São Paulo.
Anterior sepal of Xyris tortula © Suzana Martins, Instituto de Botânica de São Paulo.
Detail of the flower of Xyris trachyphylla © Maria das Graças Lapa Wanderley, Instituto de Botânica de São Paulo.