Flora of North America species comparison

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Loasaceae

Petalonyx

blazing-star family, loasa family, stickleaf family

sandpaper-plant
Habit Herbs, subshrubs, shrubs, [or trees], annual, biennial, or perennial, evergreen (leaves withering in age), scabrid, trichomes (1) unbranched and smooth, knobby, notched, or antrorsely or retrorsely barbed, (2) dendritic, and/or (3) stinging. 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

alternate [opposite], simple;

stipules absent;

petiole present or absent;

blade sometimes lobed, margins entire, serrate, dentate, or crenate;

venation pinnate, basal secondary veins commonly present.

cauline;

petiole present or absent;

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

terminal, cymes, thyrses, racemes, panicles, or flowers solitary.

racemes or panicles;

peduncle inconspicuous.
Pedicels

not elongating in fruit.
Flowers

bisexual, usually radially symmetric, rarely bilaterally symmetric (by bilateral symmetry of corolla, androecium, or gynoecium);

perianth and androecium epigynous;

hypanthium adnate to ovary proximally and free distally, or completely adnate to ovary;

sepals 5, radially symmetric, distinct or connate basally;

petals 5, radially or bilaterally symmetric, distinct or connate, sometimes postgenitally coherent;

nectary absent or present, distal on ovary;

stamens 5–150+, distinct, free or adnate to petal bases, bilaterally or radially symmetric;

anthers dehiscing by longitudinal slits;

staminodes absent or present, sometimes petaloid and petals appearing to be 6+;

pistil 1, 3–7-carpellate, ovary inferior, 1-locular, placentation parietal, subapical, or apical;

ovules 1–60+ per locule, anatropous (epitropous);

style 1;

stigma 1, 2–5(–7)-lobed (lobes usually as many as carpels, except in pseudomonomerous Gronovioideae).

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

capsules, dehiscence by apical valves [splitting longitudinally], or cypselae, sepals or sepals and petals persisting.

cypselae, ±clavate, straight;

sepals persistent.
Seeds

1–60+ per fruit.

1, ovoid.
x

= 23.

Loasaceae

Petalonyx
Distribution
North America; Mexico; Central America; South America; sw Asia (w Arabian Peninsula); Africa; Atlantic Islands (Cape Verde); Pacific Islands
[BONAP county map]
map from USDA
w United States; n Mexico
[BONAP county map]
Discussion

Genera 20, species ca. 350 (4 genera, 94 species in the flora).

Loasaceae are in Cornales and are the sister family of Hydrangeaceae. The two families likely diverged in western North America or Mexico in the Late Cretaceous to Paleocene, 92–58 million years before present (J. J. Schenk and L. Hufford 2010). Most extant species of Loasaceae in western North America date to the Oligocene or more recent times, with the Miocene and later periods being especially rich phases for speciation (Schenk and Hufford; J. Grissom and Hufford, unpubl.). In Loasaceae, Eucnide and Schismocarpus S. F. Blake, a genus restricted to southern Mexico, are the earliest diverging lineages, and the cliff-dwelling habits of these two genera may be plesiomorphic for the family (Hufford et al. 2003). The species-rich genus Mentzelia is well supported as the sister of a clade that consists of the taxonomically depauperate genera Cevallia, Fuertesia Urban, Gronovia Linnaeus, and Petalonyx. Phylogenetic studies support the monophyly of subfamilies Gronovioideae Fenzl and Loasoideae Gilg as conceived by I. Urban and E. Gilg (1900), but their early concept of Mentzelioideae as including both Eucnide and Mentzelia (and also Schismocarpus according to S. F. Blake 1918b; Gilg 1925b) is paraphyletic (Hufford et al.). To enable classification based on monophyly, circumscription of Mentzelioideae should be restricted to Mentzelia. The Mentzelia plus Gronovioideae clade is sister to the more taxon rich subfam. Loasoideae, which is especially prevalent in Andean South America (Hufford et al.).

(Discussion copyrighted by Flora of North America; reprinted with permission.)

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.

Etymology: Greek petalon, petal, and onyx, claw, alluding to distinctive petal morphology

(Discussion copyrighted by Flora of North America; reprinted with permission.)
Parent taxa Loasaceae
Subordinate taxa
Cevallia, Eucnide, Mentzelia, Petalonyx
P. linearis, P. nitidus, P. parryi, P. thurberi
Key
1. Stamens 5; seeds 1 per fruit; fruits cypselae.
→ 2
2. Inflorescences headlike thyrses, peduncles to 1 dm; perianth whorls similar, sepals and petals white to yellowish abaxially, yellow adaxially, linear-lanceolate; petals densely hairy on both surfaces; stamen filaments dorsiventrally flattened, linear, shorter than anthers; anthers with distal connective extension; stigmas densely hairy.
Cevallia
2. Inflorescences racemes or panicles, peduncles inconspicuous; perianth whorls differentiated, sepals green, lanceolate, petals white, spatulate; petals glabrous except hairy abaxially on midribs; stamen filaments filiform, longer than anthers; anthers without distal connective extension; stigmas papillate.
Petalonyx
1. Stamens 8–50+; seeds (1–)2–60+ per fruit; fruits capsules.
→ 3
3. Pistils 3-carpellate; stigmas 3-lobed.
Mentzelia
3. Pistils 5–7-carpellate; stigmas 5–7-lobed.
→ 4
4. Hypanthium completely adnate to ovary; petals connate proximally to 1/2+ length; stamen filaments filiform; pedicels elongating in fruit; seeds cylindric to ovoid, to 1 mm, not winged.
Eucnide
4. Hypanthium adnate to ovary proximally, free distally; petals distinct or connate basally; 5 outermost stamen filaments dorsiventrally flattened, spatulate; pedicels not elongating in fruit; seeds dorsiventrally flattened, 2.3–4 mm, winged.
Mentzelia
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
Name authority Jussieu A. Gray: Pl. Nov. Thurb., 319. (1854)
Source FNA vol. 12, p. 491. Treatment author: Larry Hufford. FNA vol. 12, p. 543. Treatment author: Larry Hufford.
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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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