Flora of North America species comparison

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Petalonyx

sandpaper-plant
Habit Subshrubs or shrubs; trichomes (1) pointed with surfaces ± smooth, notched, or antrorsely barbed, and (2) retrorsely barbed along shaft and at apex.
Stems

erect or spreading.
Leaves

cauline;

petiole present or absent;

blade ovate, elliptic, lanceolate, or falcate, unlobed, margins dentate, serrate, crenate, or entire.
Inflorescences

racemes or panicles;

peduncle inconspicuous.
Pedicels

not elongating in fruit.
Flowers

hypanthium adnate to ovary proximally, free distally;

perianth whorls differentiated;

sepals green, connate basally, lanceolate, shorter than petals;

petals white, distinct or connate, spatulate or obovate, erect proximally, spreading to divaricate distally (corolla salverform or appearing so), glabrous except hairy abaxially on midribs;

nectary distal on ovary;

stamens 5, exserted, filaments monomorphic, filiform, longer than anthers;

anthers without distal connective extension;

staminodes absent [present];

pistil pseudomonomerous, placenta subapical;

stigma lingulate, 2-lobed, papillate.
Fruits

cypselae, ±clavate, straight;

sepals persistent.
Seeds

1, ovoid.
x

= 23.

Petalonyx
Distribution
from USDA
w United States; n Mexico
[BONAP county map]
Discussion

Species 5 (4 in the flora).

Petalonyx belongs to subfam. Gronovioideae, which is characterized by relatively small flowers that have five stamens, one ovule, and indehiscent fruits. Petalonyx is most closely related to a clade that consists of Cevallia, Fuertesia Urban, and Gronovia Linnaeus (L. Hufford et al. 2003). Petalonyx crenatus A. Gray ex S. Watson, from Coahuila, Mexico, is the only species of the genus known only from outside the flora area; it can be distinguished from the species treated here by having two anther-bearing stamens and three shorter staminodes, rather than having five anther-bearing stamens.

(Discussion copyrighted by Flora of North America; reprinted with permission.)
Key
1. Leaf blades usually elliptic, sometimes falcate, to 5 mm wide, margins entire; petal claws distinct; stamens exserted distally (not laterally between petal claws).
P. linearis
1. Leaf blades ovate, or if elliptic then to 15–30 mm wide, margins usually serrate, dentate, or crenate, sometimes entire; petal claws postgenitally distally coherent; stamens exserted laterally through slits between petal claws.
→ 2
2. Petioles absent; leaf blades with marked size dimorphism, much larger on main stems than on fertile branches; petals to 6.5 mm.
P. thurberi
2. Petioles 0.5–4 mm; leaf blades without marked size dimorphism; petals 6–15 mm.
→ 3
3. Inflorescences 10–30-flowered; petals 6–11 mm; branches of current season 11–37 cm.
P. nitidus
3. Inflorescences 35–65-flowered; petals 10–15 mm; branches of current season to 13 cm.
P. parryi
Source FNA vol. 12, p. 543. Author: Larry Hufford.
Parent taxa Loasaceae
Subordinate taxa
P. linearis, P. nitidus, P. parryi, P. thurberi
Name authority A. Gray: Pl. Nov. Thurb., 319. (1854)
Web links 
Unless otherwise noted, all data comes from the online version of the Flora of North America, who have made most of their content available via a Creative Commons license (CC BY 4.0).



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