Styrax americanus
Styrax platanifolius
American snowbell, mock-orange, snowbell
sycamoreleaf snowbell
petiole 2–6 mm;
blade with 5–8 secondary veins, elliptic or broadly elliptic to obovate or nearly ovate, 1.2–10 × 0.6–5.7 cm, largest blades on sterile shoots 2–5.7 cm wide, margins of at least some leaves denticulate to serrate, rarely also lobed, longest arms of abaxial hairs 0.1–0.2 mm.
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.
4–10(–14) mm, longer than calyx.
4–9 mm, 1.3–2.3 times as long as calyx.
calyx 2.5–4 × 2.5–4.5 mm;
corolla 11–16 mm, tube 1.5–3 mm, lobes 5(–6), imbricate or subinduplicate-valvate in bud, strongly reflexed, elliptic to narrowly elliptic, 7–14 × 1–5 mm;
filaments distinct beyond adnation to corolla.
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.
globose, 7–9 × 7–9 mm (broader when 2–3-seeded), gray stellate-pubescent, dehiscent nearly or completely to proximal end, broadly exposing seed(s);
fruit wall 0.3–0.4 mm thick.
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.
-terminal inflorescences 2–5-flowered or solitary flower, 2–3.5 cm;
axillary flowers present on at least some shoots (subtending leaves often reduced).
-terminal inflorescences 2–7-flowered or solitary flower, 2–5 cm;
axillary flowers absent.
= 16.
Styrax americanus
Styrax platanifolius
Styrax grandifolius is partly sympatric with S. americanus, and molecular data indicate that it is a close relative (P. W. Fritsch 2001). The two species are separated ecologically, with S. americanus occupying lower, moister sites (G. J. Gonsoulin 1974). Hybridization between the two is not apparent.
Some authors have recognized plants with more densely pubescent new shoots, leaves, and inflorescences and shorter pedicels as a distinct taxon, at either the specific or infraspecific level (J. K. Small 1933; A. J. Rehder 1940; G. J. Gonsoulin 1974). The most densely pubescent plants occur in the southernmost portion of the range of the species; intermediates between the two extremes are abundant. The character differences that separate the taxa are here considered taxonomically inconsequential.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
Subspecies 5 (4 in the flora).
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.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
1. Leaf blades with abaxial surface nearly glabrous or visible through pubescence | → 2 |
1. Leaf blades with abaxial surface completely covered and obscured by pubescence | → 3 |
2. Leaf blades glabrous except for scattered, orange-brown or dark-brown, stalked, stellate hairs abaxially on some; pedicels and calyces glabrous. | subsp. platanifolius |
2. Leaf blades with scattered, white, stellate pubescence in addition to scattered, orange-brown or dark-brown, stalked, stellate hairs abaxially on some; pedicels and calyces with white, stellate hairs. | subsp. stellatus |
3. Young twigs faintly glaucous; leaf blades glabrous adaxially; styles pubescent from proximal end to ca. 15-35% of total length; abaxial surface of leaf blades, pedicels, and calyces white stellate-tomentose. | subsp. texanus |
3. Young twigs stellate-pubescent; leaf blades stellate-pubescent adaxially; styles pubescent from proximal end to ca. 60-80% of total length; abaxial surface of leaf blades, pedicels, and calyces white stellate-lanate. | subsp. youngiae |
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