7. Croton willdenowii G.L. Webster (common rushfoil)
Crotonopsis elliptica Willd.
Map 1662, Pl.
monoecious, moderately to densely pubescent with small, peltate, scalelike
trichomes (except on the upper surface of the leaf blades), these with a small,
raised, brown attachment point and a relatively broad, thin, white body, the
slender, stellate extensions forming a minute fringe around the margins, this
appressed and not appearing fuzzy; the upper surface of the leaves with
relatively dense, small, overlapping, stellate hairs, the often unequal
branches 0.6–1.0 mm long. Stems 8–40 cm long, usually sparsely
alternately branched. Leaves alternate, sessile or short-petiolate, the petiole
without large, saucer-shaped glands at the tip. Leaf blades
0.7–2.0(–3.0) cm long, linear to narrowly ovate, angled or
short-tapered at the base, rounded to angled or short-tapered to a usually
sharply pointed tip, the margins entire, the undersurface paler than the upper
surface. Inflorescences axillary, mostly short, loose spikes with 1 or 2
pistillate flowers at the base and several staminate flowers toward the tip.
Staminate flowers with the calyx deeply (4)5-lobed, 0.8–1.1 mm long;
the petals (4)5, 0.6–1.0 mm long, white; the stamens 4–6.
Pistillate flowers with the calyx 0.8–1.1 mm long at flowering, becoming
very slightly enlarged at fruiting, (4)5-lobed; the petals absent; the ovary
1-locular, the 3 styles shallowly 2-lobed toward the tip. Fruits
2.5–3.0 mm in length and diameter, elliptic to oblong-ovate in outline,
slightly flattened, 1-seeded, indehiscent, thin-walled. Seeds 2.5–3.0
mm long, elliptic to oblong-ovate in outline, slightly flattened, the caruncle
south of the Missouri River (eastern U.S. west to Iowa, Kansas, and Texas). Glades, ledges and tops of bluffs, and openings of dry upland forests; also old
fields; usually in nutrient-poor acidic soils.
This is the more
widespread of the two rushfoils in Missouri. Previously, it and C. michauxii
were classified into a separate genus of two species, Crotonopsis, based
on their 1-seeded, indehiscent fruits. However, Webster (1992) argued that Crotonopsis
represents merely a specialized subgroup within Croton related to the
group of species that includes C. monthogynous, which has two-seeded
fruits. In combining the genera, he found it necessary to coin replacement
names for both species, as the original epithets from Crotonopsis
already were in use for other species of Croton (C. ellipticus
Geiseler and C. linearis Jacq.). Websters view has been
supported by preliminary molecular phylogenetic analyses (Berry et al., 2005),
in which the two species of former Crotonopsis are nested within a more
derived lineage within Croton.