Horkelia tenuiloba
Horkelia rydbergii
Santa Rosa, Santa Rosa horkelia, Sonoma horkelia, thin-lobed, thin-lobed horkelia
Rydberg's horkelia
ascending to erect, 1–4 dm, hairs ± spreading.
ascending to erect, (1–)2–7 dm, hairs ascending to appressed.
weakly planar to ± cylindric, 5–15(–20) × 0.5–1.5 cm;
stipules entire;
leaflets 8–16(–20) per side, ± overlapping especially distally, cuneate to flabellate, 3–10 × 2–10 mm, 1/2 to nearly as wide as long, divided 1/2–3/4+ to midrib into 3–8 linear to narrowly oblanceolate or narrowly elliptic lobes, sparsely villous at least marginally, often with a tuft of hairs apically.
± planar, (4–)8–20(–30) × 0.8–2(–3) cm;
stipules entire;
leaflets 7–14 per side, separate to ± overlapping at least distally, cuneate to flabellate, (3–)5–15(–22) × 3–10(–15) mm, ± 1/2 to as wide as long, divided ± 1/3 to midrib into (3–)5–10 acute to obtuse teeth, densely (to sparsely) strigose or pilose.
2–5.
(2 or)3–6(–8).
open to congested, flowers arranged individually and in glomerules, these sometimes subcapitate.
± open to congested, flowers arranged individually or in glomerules.
1–6 mm.
(1–)2–8 mm.
10 mm diam.;
epicalyx bractlets narrowly to broadly lanceolate, 1–3 × 0.5–1 mm, slightly shorter than sepals, entire;
hypanthium 1–1.2 × 2.5–4.5 mm, less than 1/2 as deep as wide, interior pilose;
sepals spreading to reflexed, lanceolate, 3–5 mm;
petals oblanceolate, 2.5–4.5 × 1.5 mm, apex emarginate;
filaments (1–)1.5–2 × 0.5 mm, anthers 0.4–0.6 mm;
carpels 10–25;
styles 1.8–2.2 mm.
10–15 mm diam.;
epicalyx bractlets lanceolate to narrowly elliptic, 2–3.5(–4) × 0.5–1 mm, ± 3/4 length of sepals, entire;
hypanthium 1–1.5(–2) × 2.5–4.5(–6) mm, less than 1/2 as deep as wide, interior pilose;
sepals spreading to ± reflexed, lanceolate, (2.5–)3–5(–5.2) mm;
petals oblong to oblanceolate, 4–5.5 × 1.2–2.5 mm, apex rounded to truncate or slightly emarginate;
filaments 0.5–2 × 0.5–1 mm, anthers 0.6–1 mm;
carpels 20–50(–120);
styles 2–4 mm.
light brown, 1.5 mm, smooth or slightly rugose.
light to dark brown, 1–1.5 mm, smooth or roughened.
= 28.
Horkelia tenuiloba
Horkelia rydbergii
Of conservation concern.
Horkelia tenuiloba occurs on the western edges of the northern Coast Ranges in Marin, Mendocino, and Sonoma counties. Populations from San Luis Obispo formerly included in this species now are part of H. yadonii. A specimen (M. K. C[urran], July 5, 1885, UC) unequivocally of H. tenuiloba purportedly from San Luis Obispo is in all likelihood mislabeled with respect to locality.
Horkelia tenuiloba is commonly associated with seral openings in chaparral and woodlands and might be dependent on periodic disturbance by fire.
W. L. Jepson (1909–1943, vol. 2) used Potentilla stenoloba (1895) for the species encompassing the types of Horkelia tenuiloba and P. micheneri. The epithet micheneri (1893) has priority at species rank within Potentilla, since P. tenuiloba (Torrey) Greene is a later homonym of P. tenuiloba Jordan.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
Horkelia rydbergii occurs in the Transverse Ranges of Kern, Los Angeles, San Bernardino, and Ventura counties. Reports from farther north (as H. bolanderi var. parryi) are referable to H. marinensis, H. yadonii, or, possibly, H. cuneata. Although there has been occasional nomenclatural confusion between this taxon (as H. bolanderi var. parryi) and H. parryi Greene, the two are taxonomically and geographically distinct.
Plants in the Mount Pinos–Lockwood Valley area of Kern and Ventura counties, and on Frazier Mountain, are distinctly gray with an abundance of tightly curled hairs. The leaves tend to be relatively short (to 8 cm) with relatively small leaflets (3–6 mm) on the basal leaves. Stems are relatively short (to 3 dm), and the fruits are dark brown, distinctly rugose, and 1.3–1.5 mm. This phase (including the type of Horkelia rydbergii) abruptly gives way to a grayish green phase with a slightly less dense, pilose indument in the San Bernardino and San Gabriel mountains. Here the plants tend to have larger basal leaves (to 30 cm) and leaflets (5–12 mm), longer stems (to 7 dm), and fruits that are a lighter brown, mostly smooth, and 1–1.2 mm. This phase in turn grades into even less densely hairy plants near Bear Lake, where the type of H. bolanderi var. parryi was obtained.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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