Sida spinosa L.
CC = *
CW = 3
MOC = 80
Family - Malvaceae
Habit - Perennial forb.
Stems - Ascending to erect, to 60 cm, moderately to densely pubescent with minute stellate hairs.
Leaves - Alternate, simple, petiolate, stipulate. Petioles longer than the axillary flower stalks. Leaf blades 0.5-5.0 cm long, linear to ovate, the base rounded to truncate or shallowly cordate, the margins toothed, glabrous or pubescent with stellate hairs on the upper surface, pubescent with stellate hairs on the undersurface. Stipules persistent, linear.
Inflorescences - Terminal and axial, solitary flowers or small clusters.
Flowers - Calyces 5-7 mm long, the 5 lobes keeled, triangular, angled to a sharply pointed tip, pubescent with minute stellate hairs. Petals 5, 4-6 mm long, the tips strongly asymmetric, broadly rounded with a shorter, shallowly concave, notched or single-toothed portion toward one side, the margin otherwise more or less entire, yellow to yellowish orange. Stamens numerous, the staminal column circular in cross-section, without a low crown of teeth at the tip, the anthers yellow. Pistils with 5 locules and style branches, the carpels arranged in a ring. Styles fused most of their length, each branch with a globose terminal stigma.
Fruits - Schizocarps breaking into 5 mericarps, these 3-5 mm long, wedge-shaped, brown to dark brown, with a pair of short erect beaks toward the tip, the dorsal surface broadly rounded to somewhat flattened or with a shallow longitudinal groove, oblong to kidney-shaped in profile, minutely pubescent with stellate and fasciculate simple hairs toward the tip, differentiated into a sterile upper cell and a lower cell containing 1 seed. Seeds 2.0-2.5 mm long, ovate with a small notch at the tip, the surfaces glabrous, brown to dark brown.
Flowering - June - October.
Habitat - Streambanks, pond margins, roadsides, railroads, crop fields, pastures, open disturbed areas.
Origin - Native to the New and Old World tropics.
Lookalikes - None close.
Other info. - This weedy species can be found throughout Missouri and across the southeastern quadrant of the continental U.S. The plant can be identified by its small yellow flowers, short peduncles, and hairlike stipules. Stipules at the base of well-developed, mature plants become hardened and spine-like, giving the plant its common name "Prickly Sida." The plant is most commonly found in disturbed areas. Although its flowers are generally small and inconspicuous, they have the same general architecture as the large flowers of Hibiscus, which is in the same family.
Photographs taken off Lee Rd 10, Lee County, AL., 8-28-04 (DETenaglia); also at Crowley's Ridge Conservation Area, Stoddard County, MO, 8-14-2009, Marais Temps Clair Conservation Area, St. Charles County, MO, 8-1-2018, along the Katy Trail near Dutzow, Warren County, MO, 9-29-2020, and near Labadie, Franklin County, MO, 10-1-2020 (SRTurner).