Horkelia sect. Horkelia
Horkelia tenuiloba
Santa Rosa, Santa Rosa horkelia, Sonoma horkelia, thin-lobed, thin-lobed horkelia
decumbent or ascending to erect, (0.5–)1–10(–12) dm.
ascending to erect, 1–4 dm, hairs ± spreading.
usually planar, sometimes ± cylindric;
stipules usually entire, sometimes basally lobed;
leaflets (1–)3–16(–20) per side, separate to overlapping, divided ± 1/6–3/4+ to midrib into 3–30(–60) teeth or lobes not restricted to apex.
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.
2–5.
open to congested, flowers arranged individually, in usually non-capitate glomerules, and/or in corymbiform clusters.
open to congested, flowers arranged individually and in glomerules, these sometimes subcapitate.
remaining straight, 1–30(–40) mm.
1–6 mm.
epicalyx bractlets narrowly elliptic-lanceolate to broadly ovate, 0.5–3 mm wide, usually entire, sometimes toothed;
hypanthium interior pilose or glabrous;
sepals acute;
petals white, oblong-oblanceolate to round, apex obtuse to truncate to emarginate;
filaments white, glabrous, anthers longer than wide;
carpels 10–200(–220).
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.
0.8–2 mm, usually smooth or slightly rugose, sometimes merely roughened.
light brown, 1.5 mm, smooth or slightly rugose.
= 28.
Horkelia sect. Horkelia
Horkelia tenuiloba
Species 9 (9 in the flora).
Section Horkelia encompasses the species that are most commonly encountered in heavily populated areas of California. Plants are notably glandular-viscid (unless obscured by dense vestiture) and have a distinctive resinous odor.
Previous revisions (for example, P. A. Rydberg 1908c; D. D. Keck 1938) have placed Horkelia frondosa (here treated as H. californica var. frondosa) at the beginning, implying that this is the least derived expression within the genus. Such an assumption is based on its gross resemblance to sympatric members of Drymocallis; molecular evidence (T. Eriksson et al. 1998; M. Lundberg et al. 2009; C. Dobeš and J. Paule 2010) confirms that this similarity is superficial. If, as speculated above, species composing sect. Hispidulae are relicts of the original radiation, then H. californica var. frondosa is actually one of the more derived members of the genus. Species within sect. Horkelia have been ordered here according to that interpretation.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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.)
1. Leaflets 1–3 per side, sparsely short-pilose to glabrate, (15–)20–30-toothed 1/6–1/4 to midrib; petals obovate to round, (3–)4–7 mm wide. | H. truncata |
1. Leaflets (3–)5–16(–20) per side, hairy, 3–15(–30)-toothed or -lobed (collectively 10–60-toothed in H. californica) 1/6–3/4+ to midrib; petals narrowly obovate or oblanceolate to elliptic or oblong, 1–3(–4) mm wide | → 2 |
2. Hypanthia 3–5.5 mm, 1/2 to nearly as deep as wide; epicalyx bractlets 4–6(–8) mm, ± equal to sepals, entire or toothed. | H. californica |
2. Hypanthia 1–2(–3) mm, less than 1/2 as deep as wide (except H. clevelandii); epicalyx bractlets 1–4(–5) mm, shorter than sepals, entire | → 3 |
3. Leaflets ± elliptic to obovate, divided less than 1/3 to midrib into (5–)10–15 teeth; epicalyx bractlets 1.5–3 mm wide. | H. cuneata |
3. Leaflets cuneate or flabellate to ovate or nearly round, divided (1/5–)1/3–3/4+ to midrib into 3–10(–30 in H. yadonii) teeth or lobes; epicalyx bractlets 0.5–2(–2.5) mm wide | → 4 |
4. Stems ± decumbent to ascending, 1–3.5(–4.5) dm; leaflets 5–10(–12) per side, cuneate, ± overlapping; inflorescences usually congested; plants matted; coastal. | H. marinensis |
4. Stems ascending to erect, (0.5–)1–7 dm; leaflets 6–16(–20) per side, cuneate to flabellate or nearly round, separate to ± overlapping; inflorescences open to ± congested; plants tufted to matted; coastal or interior | → 5 |
5. Epicalyx bractlets 1–2(–2.5) mm wide, lanceolate to ovate; anthers 0.8–1.2 mm; hypanthia 3–6.5 mm diam. | H. yadonii |
5. Epicalyx bractlets 0.5–1(–1.5) mm wide, narrowly elliptic to broadly lanceolate; anthers 0.4–1 mm; hypanthia 2–4.5(–6) mm diam | → 6 |
6. Stems: hairs ascending to appressed; plants usually grayish to grayish green; hypanthium interior pilose | → 7 |
6. Stems: hairs ± spreading; plants green to grayish; hypanthium interior glabrous or pilose | → 8 |
7. Carpels 20–50(–120); styles 2–4 mm; basal leaves (4–)8–20(–30) cm; Transverse Ranges, s California. | H. rydbergii |
7. Carpels 10–20(–27); styles (1–)1.5–2 mm; basal leaves 3–8(–9) cm; Coast Ranges, n California. | H. bolanderi |
8. Leaflets divided 1/2–3/4+ to midrib into linear to narrowly oblanceolate or narrowly elliptic lobes; hypanthium interior pilose; n Coast Ranges, California. | H. tenuiloba |
8. Leaflets divided 1/3 to midrib into acute to obtuse teeth; hypanthium interior glabrous; Peninsular Ranges, s California. | H. clevelandii |
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