4. Styrax platanifolius Engelmann ex Torrey, Smithsonian Contr. Knowl. 6(4): 4. 1853.
Shrubs, to 6 m, not suckering from roots. Leaves: petiole 6-20 mm; blade with 5-6 secondary veins, depressed-orbiculate or broadly ovate, 4.5-9(-12) × 4.2-9(-11.5) cm, margins entire, coarsely toothed, or 3-lobed, longest arms of abaxial hairs to 1 mm. False-terminal inflor-escences 2-7-flowered or solitary flower, 2-5 cm; axillary flowers absent. Pedicels 4-9 mm, 1.3-2.3 times as long as calyx. Flowers: calyx 3-5(-6) × 4.5-5.5 mm; corolla 12-21 mm, tube 3-4 mm, lobes 5-6, imbricate in bud, slightly reflexed, elliptic, 11-18 × 3-7 mm; filaments connate 1-6 mm beyond adnation to corolla. Capsules globose, 7-10 × 7-11 mm (broader when 2-3-seeded), grayish white stellate-pubescent, dehiscent nearly or completely to proximal end, broadly exposing seed(s); fruit wall 0.3-0.5 mm thick.
Subspecies 5 (4 in the flora): Tex.; n Mexico (Coahuila, Nuevo León, Tamaulipas).
The treatment presented here is based on the morphological and molecular analyses of P. W. Fritsch (1996, 1997).
The only subspecies of Styrax platanifolius to occur outside the flora area is subsp. mollis P. W. Fritsch, from Nuevo León and Tamaulipas, Mexico. It grows in wooded canyons along the eastern escarpment of the Sierra Madre Oriental. All five subspecies are narrow endemics; of the four subspecies in the flora, three (subspp. platanifolius, stellatus, and texanus) occur only in the Edwards Plateau region of Texas; the fourth (subsp. youngiae) is known only from the Davis Mountains of western Texas and from northern Coahuila, Mexico.