Mimosa nuttallii (Nutt.) B.L. Turner, nuttall sensitive–briar, catclaw schrankia, catclaw sensitive–briar, shame–boy. Perennial herb, trailing, spinescent, not rosetted, several–stemmed from base, branches long (to 1200 mm) with axillary inflorescences, procumbent, spreading, and trailing close to ground and on neighboring plants; andromonoecious; shoots with only compound cauline leaves, secondary leaflets folding together when touched (thigmotropic), internodes long and armed with sharp prickles.
Stems 8–ridged, to 3 mm diameter, with 3 ridges descending from each leaf, tough, ridges red and furrows green, having backward–leaning prickles and sessile glandular hairs in furrows.
Leaves helically alternate, even–2–pinnately compound in range with 5—7 pairs of primary leaflets (pinnae) spaced 7—13 mm apart, primary leaflet having to 14 pairs of secondary leaflets, petiolate with pulvinus, with stipules; stipules 2, attached to leaf base below pulvinus, threadlike, 2—4(—7) mm long, short–hairy; petiole pulvinus narrower than petiole axis, above pulvinus 4–ridged and 4–sided (not channeled), with arched short hairs, having slightly depressed glands along upper side, lower side with prickles to 2 mm long; rachis 4–sided, to 63 mm long + acuminate extension 1.5—3 mm long, with 10+ prickles on lower side; stipels 2 subtending petiolule on upper side, straight, 0.6—0.8 mm long, reddish; petiolule pulvinus ascending; rachilla to 23 mm long, with prickles on lower side; secondary petiolule pulvinus, 0.25—0.3 mm long, light green; blades of secondary leaflets oblong (elliptic), 1.8—5.5 × 0.7—1.4 mm, asymmetric at base, entire and short–ciliate on margins, obtuse with short point at tip, 3–veined at base, venation visible but not raised until drying.
Inflorescence headlike spike, axillary, 1—2 per node and branch appearing like a leafy cymelike array, spike on long peduncle, peduncle > petiole, spike hemispheroid, 21—24 mm across (exserted stamens), 75+–flowered, flowers helically alternate, subsessile, lower flowers staminate and upper flowers bisexual; bracteate; peduncle ridged, to 60 mm long increasing 2× in fruit, having numerous backward–curved prickles; rachis cylindric, ca. 5 × 1.5 mm, with glandular hairs and somewhat viscid; bractlet subtending pedicel spoon–shaped and cupped, 0.5—1 mm long, green and purple–red at tip, sparsely short–ciliate on margins; pedicel < 0.3 mm long, white, glabrous.
Flower bisexual, radial, ca. 3 mm across (stamens); receptacle with nectary at base of stalk of pistil; calyx 5–toothed, bell–shaped, 0.8 mm long, with gland on each tooth; corolla 5–lobed, funnel–shaped; tube 2 mm long, 1.5 mm wide at orifice, translucent but green along 5 veins, low 5–ridged; lobes acute–oblong, ± 1.5 × 0.5 mm, green with red on tips; stamens 10, free; filaments ascending, subequal and ± straight, 9—10 × 0.15 mm, orchid; anthers dorsifixed–versatile, dithecal, 0.3—0.4 mm, pale light yellow, longitudinally dehiscent; pollen pale light yellow; pistil 1, concealed (included), short–stalked; ovary superior, fusiform–oblong to fusiform, 1.4—1.7 × 0.35 mm, pale green or greenish, dimpled on sides with lines of papillae, 1–chambered with 10—20 ovules on upper side; style often coiled, to 2.5 mm long, white at base to orchid above; stigma terminal, recessed.
Fruit pod (legume), to 5 ascending to spreading from upper portion of rachis, dehiscent by lengthwise strips (ridges), in range 10— < 20–seeded in tight row, linear and somewhat cylindric, 45—100 × 3—3.5 mm and beak to 3 mm long, spinescent with rows of prickles (including on lower beak), especially along ridges and minutely speckled, ridges base–to–tip and 0.5—1 mm high, prickles slight curved (straight–tipped), ± 1.5 mm long; stalk ca. 2 mm long and pedicel < 1 mm long.
Seed ellipsoid or oblong (when not crowded) to trapezoidal or parallelogram–like (tightly packed), 3.8—7.5 × 2.8—3 mm, ± glossy dark brown, with short, subterminal hilum.
A. C. Gibson