| # The Families of Angiosperms |

L. Watson and M.J. Dallwitz

### Triuridaceae Gardn.

Habit and leaf form. Achlorophyllous, pallid or purplish herbs (lacking stomata, raphides and silica bodies, with fungal mycelium situated outside the plant and inside its subterranean parts). Leaves much reduced. Plants with roots; parasitic; mycoheterotrophic (mycotrophic, with intracellular fungal tissues digested by the parasite); not green; parasitic on roots of the host. Without conspicuous aggregations of leaves. Mesophytic. Leaves minute, or small; alternate; membranous; not imbricate; sessile; non-sheathing; simple. Lamina entire; one-veined; without cross-venules.

Leaf anatomy. Stomata absent. The mesophyll without crystals. Foliar vessels absent.

Axial (stem, wood) anatomy. Secondary thickening absent. The axial xylem without vessels.

Root anatomy. Root xylem without vessels (Andruris).

Reproductive type, pollination. Unisexual flowers present, or absent (rarely). Plants monoecious, or dioecious, or polygamomonoecious (?), or hermaphrodite (rarely — in some Sciaphila species). Pollination probably entomophilous.

Inflorescence, floral, fruit and seed morphology. Flowers aggregated in ‘inflorescences’; in racemes (usually), or in cymes. The ultimate inflorescence units racemose (usually), or cymose. Inflorescences terminal; sympodial in Triuris, otherwise racemes. Flowers bracteate; small; regular; not exhibiting the androecium internal to the gynoecium (i.e., unlike Lacandoniaceae); cyclic; tetracyclic. Floral receptacle developing an androphore (Triuris), or developing a gynophore; not markedly hollowed. Perigone tube present (short, the lobes often reflexed).

Perianth of ‘tepals’; (3–)6(–10); joined; 1 whorled (valvate in bud); petaloid; without spots; white, or red to purple, or hyaline.

Androecium (2–)3(–6). Androecial members free of the perianth; all equal; free of one another, or coherent; 1 whorled. Androecium exclusively of fertile stamens, or including staminodes. Staminodes non-petaloid. Stamens (2–)3(–6); rather theoretically alterniperianthial (Sciaphileae), or oppositiperianthial (Triurideae); filantherous, or with sessile anthers (or, in Triuris, immersed in an androphore variously interpreted as representing receptacle or connective tissue). Anthers non-versatile; dehiscing via longitudinal slits, or dehiscing transversely (commonly), or dehiscing via longitudinal slits to dehiscing transversely (i.e., sometimes diagonally); extrorse; bilocular to four locular; tetrasporangiate (mostly), or bisporangiate (e.g. some Triuris), or bisporangiate to tetrasporangiate (often trisporangiate in Sciaphila); appendaged (by extension of the connective), or unappendaged. Endothecium developing fibrous thickenings. Anther epidermis persistent. Microsporogenesis successive. The initial microspore tetrads tetrahedral, or isobilateral. Anther wall initially with one middle layer; of the ‘monocot’ type. Tapetum glandular. Pollen shed as single grains. Pollen grains nonaperturate; 3-celled (in Sciaphila).

Gynoecium 6–50 carpelled. Carpels isomerous with the perianth, or reduced in number relative to the perianth, or increased in number relative to the perianth. Gynoecium apocarpous; eu-apocarpous; superior. Carpel stylate; with a lateral style, or with a gynobasic style; 1 ovuled. Placentation basal. Stigmas papillate (Sciaphylla, Soridium), or non-papillate (the rest). Ovules funicled; ascending; non-arillate; anatropous; bitegmic; tenuinucellate. Outer integument not contributing to the micropyle. Embryo-sac development Polygonum-type, or Fritillaria-type. Polar nuclei fusing prior to fertilization. Antipodal cells formed; 3; not proliferating; ephemeral. Synergids pear-shaped. Endosperm formation nuclear.

Fruit non-fleshy; an aggregate. The fruiting carpel dehiscent (usually), or indehiscent (Soridium); a follicle, or an achene. Seeds copiously endospermic. Endosperm oily, or not oily (starch only in Triurideae). Embryo rudimentary at the time of seed release. Testa without phytomelan; thick.

Geography, cytology. Tropical. Pantropical and subtropical. X = 11, 12, 14.

Taxonomy. Subclass Monocotyledonae. Dahlgren et al. Superorder Triuridiflorae; Triuridales. APG III core angiosperms; Superorder Lilianae; non-commelinid Monocot. APG IV Order Pandanales.

Species 80. Genera 7; Andruris, Hexuris, Hyalisma, Sciaphila, Seychellaria, Soridium, Triuris.

Illustrations. • Species of Sciaphila and Triuris: Nat. Pflanzenfam. II (1889). • Hexuris gardneri, Sciaphila tenella, Triuris hyalina: Lindley. • Sciaphila secundiflora (as S. major) and S. arfakiana (as S. clemensiae): Hook. Ic. Pl. 29 (1907). • Seychellaria magagascariensis: Humbert, Flore Madagascariensis et Comores 27 (1946). • Sciaphila janthina (as Hyalisma), and Soridium spruceanum: Miers, Trans. Linn. Soc. 21 (1855). • Sciaphila albescens, S. caudata, S. corymbosa, Soridium spruceanum, Peltophyllum luteum: Fl. Brasiliensis 3 (1840).

We advise against extracting comparative information from the descriptions. This is much more easily achieved using the DELTA data files or the interactive key, which allows access to the character list, illustrations, full and partial descriptions, diagnostic descriptions, differences and similarities between taxa, lists of taxa exhibiting or lacking specified attributes, distributions of character states within any set of taxa, geographical distribution, genera included in each family, and classifications (Dahlgren; Dahlgren, Clifford, and Yeo; Cronquist; APG). See also Guidelines for using data taken from Web publications.

Cite this publication as: ‘Watson, L., and Dallwitz, M.J. 1992 onwards. The families of flowering plants: descriptions, illustrations, identification, and information retrieval. Version: 8th June 2026. delta-intkey.com’.

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