keys to the vascular plants of east texas - Botanical Research ...

422 ALISMATACEAE
banana-like fruits are delicious, contain considerable sugar, and were converted by Chihuahua
Indians into a fermented beverage. Long fibers obtained by macerating the leaves were used in
the past to make ropes (Crosswhite 1980). m/308
Yucca tenuistyla Trel., (slender-styled), WHITE-RIM YUCCA. This very poorly known Yucca species
is found on brushlands on the Edwards Plateau and the South TX Plains and could possibly
be found on the s margin of East TX—an Austin Co. Trelease specimen cited in McKelvey
(1947) may be Y. tenuistyla, but in the words of McKelvey (1947), “the material is immature and
inadequately labelled.” The species is endemic to TX (Kartesz 1999; Carr 2002b, 2002c; Hess &
Robbins 2002). The plants are acaulescent and diminutive (to ca. 1 m tall, but usually much
less), resembling Y. arkansana but with a branched inflorescence; leaf blades 10–20 mm wide,
mostly recurving; capsules not constricted. Flowering spring. According to Hess and Robbins
(2002), the characters separating this species from Y. constricta are tenuous, and McKelvey
(1947) included it within Y. constricta “with a question.” However, these two species are usually
easily distinguished in the field. Yucca constricta is typically a much taller plant with very numerous,
straight, narrower leaves (3–)7–15 mm wide and constricted capsules. Detailed field
work is needed to determine the range and appropriate status of Y. tenuistyla. (RARE 2001,
2002b: G3S3) E
ALISMATACEAE Vent.
ARROWHEAD OR WATER-PLANTAIN FAMILY
Annual or perennial, aquatic or wet area herbs, largely glabrous, with milky sap; leaves basal,
sometimes dimorphic with different submersed (linear and bladeless) and emergent (generally
with distinct blades) forms; leaf blades entire, linear to ovate-elliptic, or triangular and with
basal lobes (= sagittate), longitudinally ribbed (midrib more prominent than others) and with
cross veins; inflorescences scapose, racemose, paniculate, or rarely umbellate, bracteate, with
flowers or branches in whorls; flowers perfect or imperfect; sepals 3, green; petals 3, white or
rarely pink, equal; stamens 6–many; pistils 15–many, of a single carpel each, on a swollen or
elongating receptacle; ovary superior with basal placentation; fruits achenes in our species, often
with stylar beaks.
AA small (ca. 80 species in 12 genera) family of aquatic or wet area plants, nearly cosmopolitan
in distribution (Haynes & Hellquist 2000a) but primarily n temperate and neotropical
with most species found in the New World. A number of species are valuable as food for wildlife
or as aquarium plants or aquatic ornamentals. Molecular analyses (e.g., Duvall et al. 1993b;
Chase et al. 2000; Fuse & Tamura 2000; Soltis et al. 2000) indicate that Alismataceae are phylogenetically
near the base of the monocotyledons—Acoraceae are the sister group to all other
monocots, with Alismataceae in the next most basal clade. The presence of unsealed carpels
(during flowering) (Kaul 1976) may be indicative of this basal position. The Limnocharitaceae
appears to be the family most closely related to Alismataceae (Haynes & Holm-Nielsen 1992;
Les & Haynes 1995; Haynes et al. 1998a) and has sometimes been submerged in the
Alismataceae (Judd et al. 1999). However, most modern treatments (e.g., Cronquist 1981;
Takhtajan 1997; Haynes 2000a; Haynes & Hellquist 2000a) separate the two families. (subclass
Alismatidae—Cronquist; order Alismatales—APG II)
FAMILY RECOGNITION IN THE FIELD: wet area or aquatic herbs with milky sap and basal, often
broad, usually distinctly petiolate leaves; flowers whorled, usually in scapose racemes or
panicles, with 3 green sepals, 3 white or rarely pink petals, and usually numerous separate pistils
(later, achenes).
REFERENCES: Small 1909; Beal 1960a; Charlton 1973; Argue 1974, 1976; Rogers 1983; Haynes 1984;
Dahlgren et al. 1985; Kaul 1985; Haynes & Holm-Nielsen 1994; Haynes et al. 1998a; Haynes &
Hellquist 2000a.