Thelesperma filifolium (Hooker) A. Gray, greenthread. Annual (persisting), taprooted, initially rosetted, several—many–stemmed at base, ± erect to ascending with canopy of heads on long peduncles, 20—70 cm tall; shoots with basal leaves and cauline leaves, foliage finely dissected, feathery, and restricted to lower half of plants, glabrous.
Stems cylindric, to 3 mm diameter (aboveground) but thicker if older stem branched belowground, internodes < 35—90 mm long, tough, light green.
Leaves opposite decussate, symmetrically 1—2(—3)–pinnately dissected having paired principal lateral lobes and with paired lateral, linear secondary lobes, petiolate with pair of leaves fused across and sheathing node, without stipules; petiole indistinct from channeled leaf axis, petiole technically 2—5 mm long, whitish, (3)5–veined, the truncate connection across node membranous and concealing node, sometimes sparsely and minutely ciliate on margin; blade broadly triangular in outline (threadlike lobes), primary and secondary blade axis channeled, below the basal primary lobes 5—25 mm long.
Inflorescence head, terminal on each principal shoot, 1—several heads in loose, open, cymelike array, head radiate, 20—45 mm across, with 8 neuter ray flowers and many bisexual disc flowers, disc 7—17 mm across, bracteate, glabrous and green parts often glaucous; peduncle cylindric, 50—150 mm long, with leaflike bract below midpoint to approaching head (= node for future heads), = diminutive leaf with threadlike segments and lobes, having bend at base, 2–veined, bracts at top of peduncle 7—8 bracts (calyculus) fused at base into rim and spreading, long–tapered, ca. 7 mm long; involucre barrel–shaped to urn–shaped truncate at base, glaucous, phyllaries 7—8 in 2 series fused 1—2 mm at base, appressed from base then bent and spreading above midpoint, ± acute–ovate, 7.5—8 × 4—4.5 mm, outer surface green with translucent narrow membranous margins, inner surface above midpoint light yellow with many fine purple–red veins converging at tip; receptacle flat, glabrous, hollow beneath receptacle, with bractlet (palea) subtending and cupping the ovary of each disc flower, palea oblong, 5—6 × 1.2—1.7 mm, scarious with 2 fine, pale orange to red parallel stripes along yellowish midrib to midpoint or approaching tip, having scattered, inconspicuous glands in colorless tissue, abscising clinging to fruit.
Ray flower bilateral, 4—10 mm across; calyx (pappus) vestigial rim with a pair of minute bumps and minute hairs; corolla 3–lobed; tube shallowly 3–ribbed, 2.2—2.5 × 0.5—0.6 mm; limb fan–shaped, (12—)14—24.5 × 4—10 mm, golden yellow, somewhat jagged on outer margin, finely parallel–veined with short hairs on lower surface along veins; stamens absent; pistil 1, sterile; ovary inferior, 3–sided flat on outer side, ca. 5 × 0.8—0.9 mm, whitish, thin front–to–back, papillate along edges and barely papillate–tufted at 2 top corners; style absent.
Disc flower bisexual, radial, ca. 2 mm across, ca. 12 mm long; calyx (pappus) of 2 dwarf awns, conic and fleshy, 0.4—0.5(—1) mm long, whitish, with backward–leaning barbs, persistent; corolla 5–lobed, lacking hairs; tube straight to slightly curved, 4.5—5.5 × 0.3 mm, golden yellow, with 5 fine veins; throat bell–shaped, ca. 1.3 × 1 mm, yellowish to midpoint and red above midpoint, with 5 veins leading to sinuses; lobes suberect to ascending, acute–triangular, 1.8—2 × 0.5 mm, glossy burgundy, ± stiff; stamens 5, attached to top of corolla tube; filaments 1 mm long, golden yellow (orange–yellow); anthers fused into cylinder surrounding style, often fully exserted from corolla, basifixed, dithecal, 2—2.4 mm long including appendages at top, burgundy, appendages triangular flexed outward, 0.5 mm long; pollen golden yellow; pistil 1; ovary inferior, cylindric and often straight but outer series somewhat arched, ca. 3 × 0.4 mm long, white, glabrous, 1–chambered with 1 ovule; nectary disc surrounding base of style, 0.25 mm long, greenish; style exserted from anthers ca. 1 mm, golden yellow, 2–branched, the branches stigmatic at deltate tips conspicuously papillate, often scarcely spreading.
Fruits cypselae (achenes) of disc flowers, having papery palea and 2 dwarf awns; cypsela straight to somewhat arched, 4—6.5 × 1.1—1.4 mm, dark brown, 1 face rough, other sides conspicuously bumpy (tuberculate); awns erect, 3–sided with sloping edge to center of fruit top, 0.5—1 mm long; palea pale to light brown with a pair of darker lines parallel to a raised midrib.
A. C. Gibson