Vascular Plants of Williamson County

Marshallia caespitosa var. signata [Asteraceae]
Barbara’s buttons

Marshallia caespitosa DC. var. signata Beadle & Boynt., Barbara’s buttons. Perennial herb, fibrous–rooted, rosetted, several–stemmed at base, not branched above base, leafy at base of peduncle, to 45 cm tall; shoots with basal leaves withering at flowering and 8+ cauline leaves, appearing glabrous with microscopic hairs.

Stems

Stems conspicuously 8–ridged, to 3.5 mm diameter, with 3 coarse ridges descending from each leaf, having a large bump on each ridge at leaf base, along ridge with upward–arching hairs < 0.3 mm long.

Leaves

Leaves helically alternate, simple, petiolate (basal leaves) and sessile (cauline leaves), without stipules; petiole partially sheathing, thin, and white at base, indistinct from blade; blade linear or narrowly oblanceolate to narrowly oblong or narrowly elliptic, < 20—95 × 3—14 mm, long–tapered (basal leaves) to tapered at base, entire, ± rounded at tip, 3(5)–veined at base with midrib sunken on upper surface and midrib or 3 principal veins raised on lower surface, when young with inchwormlike small hairs arching toward the tip and scattered sessile glandular hairs with colorless heads, stomates on both surfaces.

Inflorescence

Inflorescence head, hemispheric, of showy, discoid flowers, head in range 22—29 mm across, 100+–flowered, marginal flowers widely spreading from involucre, bracteate, with inchwormlike hairs and glandular hairs on exposed green tissues; bract subtending peduncle leaflike; peduncle ± 13–ridged descending from phyllaries, in flower 90—150 mm long increasing in fruit, with inchwormlike hairs along ridges and sessile glandular hairs in furrows; involucre hemispheric, phyllaries to 21 in several close series, appressed, subequal, narrowly lanceolate, 11—12 mm long, light green with membranous margins to 2/3, keeled with inchwormlike and sessile glandular hairs on green tissue; bractlet subtending flower (palea) grading from inner phyllaries, erect and conspicuous above flower buds, mostly linear, 9—10 × 0.6 mm, keeled with membranous margins, acute at tip (in range not notched), with fewer hairs than phyllaries; receptacle domed, glabrous, hollow beneath.

Flower

Flower bisexual, radial, 7—8 mm across; sweetly fragrant; calyx (pappus) of 5—6 scales in 1 whorl, scale ± triangular, 1.5—3.4 × 0.6—1 mm, colorless (purple rarely at base), overlapping at base, often minutely jagged at least above midpoint, with fine point at tip, persistent; corolla 5–lobed; tube + throat ca. 10 mm long, cylindric to midpoint and ca. 0.4 mm diameter, with dense arching hairs, throat funnel–shaped to 1.3 mm diameter at orifice; lobes spreading, oblong and rounded at tip, in range ± 4 × 0.7—0.8 mm, pure white or aging purplish only at base; stamens 5, fused to corolla at base of throat, exserted from corolla throat; filaments 2 mm long, white; anthers fused into cylinder surrounding style, basifixed, dithecal, 3—4.5 mm long including ovate appendages at tip, with 10 fine, purple stripes, appendages folded outward from centerline; pollen white; pistil 1; ovary inferior, wedge–shaped and 5–ribbed, 1 × 0.6—0.7 mm, green, with ascending, straight short hairs along ribs and sessile glandular hairs in furrows, 1–chambered with 1 ovule; style exserted, 9.5—10 mm long, white, nectary surrounding base of style, 0.3 mm long, and white, style 2–branched, the branches spreading above anther appendages, oblong conspicuously grooved on upper surface and papillate on lower surface

Fruits

Fruits cypselae, monomorphic, wedge–shaped and strongly 5–ribbed, 3—4 × 1.5 mm, tannish, ribs with dense strip of ascending, straight short hairs and furrows with abundant sessile, reddish glandular hairs; pappus of 5—6 ascending, colorless, triangular scales to 1.5—2.5(—3.4) mm long.

A. C. Gibson