Falfurrias milkvine

Vines, suffrutescent, not corky. Stems 1–10, twining, 30–200 cm, retrorse-puberulent with curved, eglandular trichomes. Leaves with 1 colleter on each side of petiole; petiole 0.3–0.6 cm, puberulent with curved, eglandular trichomes and incon­spicuously glandular-hirtellous; blade deltate to narrowly lanceolate, 1–2 × 0.2–0.7 cm, base truncate to shallowly cordate, with 2–4 laminar colleters, apex acute, surfaces sparsely puberulent with curved, eglandular trichomes and very inconspicuously glandular-hirtellous on veins abaxially, glabrate adax­ially. Inflorescences solitary, extra-axillary, sessile or sub­sessile, 1(or 2)-flowered. Pedicels 1–3 mm, puber­ulent with curved, eglandular trichomes and incon­spicuously glandular-hirtellous. Flowers: calyx lobes spreading, narrowly lanceolate, 2–3 mm, apex acute, sparsely puberulent with curved, eglandular trichomes and inconspicuously glandular-hirtellous; corolla yel­low­ish green abaxially, brown with green tinge adaxially, not or very faintly reticulate, cam­panulate, tube 1–2 mm, lobes ascending, lanceolate, 5–6 mm, glabrous; corona of 5 laminar segments opposite anthers, apex retuse, white with purple adaxial patch, 2.5–3 mm, greatly exceeding style apex, glabrous; apical anther appendages white, deltoid; style apex green, pentagonal-lobed, flat with central, bifid protrusion. Follicles gray-striate, lance-ovoid to fusiform, 5–8 × 0.8–1 cm, apex acuminate, smooth to moderately tuber­culate, mostly on lower two-thirds, sparsely puberulent to glabrate. Seeds tan, ovate, 6–7 × 4–5 mm, margins winged, chala­zal end scarcely erose, faces inconspic­uously rugulose; coma 2–3 cm.

Flowering Apr–Aug; fruiting Jul–Dec. Low hills or plains, rocky and clay soils, thornscrub; of conservation concern; 30–100 m; Tex.

Matelea radiata is very uncommon and possibly endemic to Brooks, Hidalgo, and Starr counties in south­ern Texas. Only three flowering specimens are known, from near Falcon Lake and La Joya, in the Lower Rio Grande Valley, and the type collection from the imprecise location of Falfurrias. Based on the restriction of all other collections to the vicinity of the Rio Grande Valley, including fruiting specimens assigned here tentatively, it is possible that the type collection was made a good deal south of Falfurrias. Similar in most respects to close relatives M. parvifolia and M. sagittifolia, M. radiata is readily differentiated by elongate white corona segments that greatly exceed the style apex. Based on scant evi­dence, it is possible that the follicles are more densely tuberculate than in the related species. It is wholly dis­junct from the range of M. parvifolia, which is found only as far east as the Big Bend region, and it is known to co-occur with M. sagittifolia only in the vicinity of Falcon Lake. Considering the rarity of M. radiata and development pressures in the Lower Rio Grande Valley, this species should be considered to be of extreme con­servation concern.