Senecio ampullaceus Hooker, texas groundsel, squaw–weed. Annual, taprooted, 1–stemmed at base, with ascending branches in flowering canopy, ± erect, 30—80 cm tall; gynomonoecious; shoots with only cauline leaves, loosely cobwebby tomentose to glabrate and aging often with few hairs.
Stems cylindric, to 13 mm diameter, with cobwebby hairs oriented lengthwise along axis.
Leaves helically alternate, simple and subsessile to sessile and clasping, without stipules; blade ovate (large leaves) to obovate, (15—)30—180 × (6—)12—120 mm, lower cauline leaves with green tissue (wings) to 3.5 mm wide along midrib, dentate margins, and acute at tip, upper cauline leaves with clasping basal lobes, minutely dentate to midblade and entire above midblade (upper cauline leaves), and obtuse at tip, pinnately veined with midrib sunken on upper surface and raised, thick, and fleshy on lower surface, lower surface sparsely cobwebby and with scattered sessile glandular hairs.
Inflorescence heads, in terminal, ± flat–topped cymelike arrays of (5—)10—30 heads, head radiate, 16—26+ mm across, in range mostly with (7—)8—10 pistillate ray flower and 40+ bisexual disc flowers, bracteate; bract subtending principal branch, lanceolate, to 28 mm long, with several teeth before midblade on margins, bract subtending secondary branchlets shorter and often with only a pair of lobes or teeth near base; bract subtending peduncle 1/2 sheathing, appressed, acuminate narrowly lanceolate to linear, 5—8 mm long, white and greenish, flared at base; peduncle low–ridged, to 25 mm long, light green, glabrate with inconspicuous glandular hairs, often with bract at midpoint (= future head), at top having 2—8 helically alternate linear bracts (calyculus) subtending and appressed to involucre, bracts 4—5 × 0.2—0.3 mm; involucre bell–shaped, 4.5—12 × 4—5 mm, becoming spheroidal at base as fruits form, phyllaries 12—14 in 1—2 series, subequal, sometimes 2 fused, strap–shaped, (5.5—)7—10 × 1—1.6 mm (2× wide if fused), yellowish green with membranous margins, sometimes having a red point on acuminate to acute tip (visible in bud), inner phyllaries wider and having rounded backs and wider membranous margins and glandular hairs on back, short–fringed at tip; receptacle flat to somewhat concave, lacking bractlets (paleae), with short crown around base of each sunken ovary.
Ray flower bilateral, ca. 4 mm across; calyx (pappus) of capillary bristles, at anthesis 3—4 mm long increasing 2× in fruit, silky white; corolla weakly 3–lobed; tube cylindric ca. 3.5 × 0.3 mm, pale green at base to yellowish light green at top, glabrous; limb strap–shaped to ± elliptic or oblong, < 7—11.5 × 3.5—4 mm, bright yellow, minute teeth at tip, glabrous; stamens absent; pistil 1; ovary inferior, cylindric, ca. 0.7 × 0.4 mm, light green, densely short–hairy, 1–chambered with 1 ovule; style exserted 1—1.5 mm, 2–branched, yellowish at base to yellow–orange above, the stigmatic branches 1 mm long.
Disc flower radial, 1—1.3 mm across; calyx (pappus) of capillary bristles, at anthesis 3—4 mm long increasing 2× in fruit, silky white; corolla 5–lobed, 5.7—6.4 mm long, glabrous; tube cylindric, 2—3.5 × 0.35 mm, white; throat narrowly funnel–shaped, ca. 2.5 mm long, 1 mm wide at orifice, yellow; lobes ovate–triangular, ± 0.7 mm long, bright yellow; stamens 5, attached to top of corolla tube; filaments 0.6—0.7 mm long, colorless; anthers fused into cylinder surrounding style, basifixed, dithecal, 2 mm long including appendages at top, appendages 0.5 mm long, bright yellow, longitudinally dehiscent; pollen yellow; nectary disc surrounding base of style, producing copious nectar in corolla tube; pistil 1; ovary inferior, cylindric, ca. 0.7 × 0.4 mm, light green, densely short–hairy, 1–chambered with 1 ovule; style at anthesis included later exserted, 2–branched, white below fork, the stigmatic branches ascending, 0.7 mm long, yellow, after exserted aging recurved.
Fruits cypselae (achenes), monomorphic, columnar, 3.5—3.9 × 0.7—0.8 mm, brown, truncate at base, 10–ribbed, with rim and somewhat depressed at top, short–hirsute with upward–pointing hairs; pappus
A. C. Gibson