Flora of North America species comparison

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Petalonyx thurberi subsp. gilmanii

Loasaceae
Photo is of parent taxon

Death Valley sandpaper plant

blazing-star family, loasa family, stickleaf family
Habit Plants to 10 dm; branches of current season to 21 cm; hairs on inflorescence-bearing stems soft, ± erect. 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.
Leaves

to 20 × 13 mm.

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.
Inflorescences

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

petals to 4.1 mm;

stamens 5–8 mm;

style 4–6 mm.

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).
Fruits

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

1–60+ per fruit.
2n

= 46.

Petalonyx thurberi subsp. gilmanii

Loasaceae
Phenology Flowering May–Sep.
Habitat Sandy washes, sand dunes.
Elevation 400–1000 m. (1300–3300 ft.)
Distribution
from FNA
CA
[BONAP county map]
North America; Mexico; Central America; South America; sw Asia (w Arabian Peninsula); Africa; Atlantic Islands (Cape Verde); Pacific Islands
[BONAP county map]
Discussion

Subspecies gilmanii is found only in Inyo County.

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

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.)
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
Source FNA vol. 12, p. 545. FNA vol. 12, p. 491. Author: Larry Hufford.
Parent taxa Loasaceae > Petalonyx > Petalonyx thurberi
Sibling taxa
P. thurberi subsp. thurberi
Subordinate taxa
Cevallia, Eucnide, Mentzelia, Petalonyx
Synonyms P. gilmanii
Name authority (Munz) W. S. Davis & H. J. Thompson: Madroño 19: 15. (1967) Jussieu
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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