Horkelia tridentata

Torrey in War Department [U.S.]

in War Department [U.S.], Pacif. Railr. Rep. 4(5): 84, plate 6. 1857.

Endemic
Treatment appears in FNA Volume 9. Treatment on page 269. Mentioned on page 259, 264, 267.

Plants mostly rosette-forming, grayish. Stems decumbent to nearly erect, 0.5–4 (–7) dm, hairs 1–3 mm proximally, glands absent or sparse distally. Basal leaves planar, 3–12 × 1–3 (–4) cm, usually sericeous to villous, sometimes glabrate adaxially; stipules entire or rarely forked or pectinate; leaflets 2–5 (or 6) per side, separate to slightly overlapping, elliptic to cuneate-oblong, (3–) 5–20 (–30) × 1.5–7 (–10) mm, (1/4–) 1/3–1/2 as wide as long, divided 1/10–1/6 or less to midrib into (0–) 3 (or 4) triangular teeth 1 mm wide, these restricted to apex. Cauline leaves 1–5; stipules 3–12 mm, entire or deeply 3–5-lobed, lanceolate to ovate. Inflorescences open to congested, flowers arranged in ± capitate glomerules or in ± corymbiform clusters. Pedicels (1–) 2–6 (–10) mm. Flowers 4–10 mm diam.; epicalyx bractlets linear to narrowly elliptic, 0.8–2 (–3) × 0.2–0.4 mm, 1/2–2/3 length of sepals; hypanthium 1–2.5 × 2–5 mm, 1/2 to nearly as deep as wide, interior glabrous or pilose; sepals moderately reflexed, abaxially green to reddish, 1.5–3 mm; petals white, sometimes tinged with pink, linear to broadly oblanceolate, (1–) 1.5–4 (–4.5) × 0.3–1.5 mm, apex acute to rounded or mucronate; filaments 0.5–2 × 0.1–0.4 (–0.8) mm, anthers 0.2–0.5 mm; carpels 5–15; styles 1–2.5 mm. Achenes light-brown, 1.5–2.5 mm, rugose.

Discussion

Varieties 2 (2 in the flora).

Rydberg established Horkelia flavescens on the basis of its more congested inflorescence, purportedly yellowish petals, and broader filaments. As noted by D. D. Keck (1938), the petals are usually white, at least when fresh, and the other characters are highly variable; he reduced H. flavescens to a subspecies of H. tridentata, which is here treated at the rank of variety. In general, var. flavescens tends to be more decumbent with a single, loosely congested flower cluster and broader petals; these characters completely overlap and can vary independently. The presence or absence of hairs on the hypanthium interior is the single most reliably diagnostic character and is the primary determiner of the geographic distributions presented here. The exception is a cluster of populations from the extreme southern end of the coastal range of var. flavescens in Colusa, Lake, and Mendocino counties, California, which have glabrous hypanthia but otherwise have all the diagnostic characters of var. flavescens. Although provisionally included here within var. flavescens, these populations may be better treated as a separate variety.

Selected References

None.

Key

1 Hypanthium interior glabrous; petals linear to oblanceolate, usually ± equal to or longer than sepals; inflorescences composed of 1+ ± capitate glomerules, these sometimes expanding with age. Horkelia tridentata var. tridentata
1 Hypanthium interior pilose (except in some North Coast Ranges of California); petals ± broadly oblanceolate, often shorter than sepals; inflorescences composed of usually 1 ± corymbiform cluster. Horkelia tridentata var. flavescens

"/2lengthofsepals" is not declared as a valid unit of measurement for this property.No values specified."dm" is not declared as a valid unit of measurement for this property.

... more about "Horkelia tridentata"
light-brown +
1.5mm +  and 2.5mm +
shorter than wide +  and longer +
0.02 cm0.2 mm <br />2.0e-4 m <br /> (0.05 cm0.5 mm <br />5.0e-4 m <br />) +
truncate +  and emarginate +
Barbara Ertter +  and James L. Reveal +
Torrey in War Department [U.S.] +
compound +  and simple +
opposite +  and alternate +
3 cm30 mm <br />0.03 m <br /> (4 cm40 mm <br />0.04 m <br />) +
3 cm30 mm <br />0.03 m <br /> (12 cm120 mm <br />0.12 m <br />) +
1 cm10 mm <br />0.01 m <br /> (3 cm30 mm <br />0.03 m <br />) +
flattened +
Tridentatae +
30 cm300 mm <br />0.3 m <br /> (40 cm400 mm <br />0.4 m <br />) +
planar +  and cylindric +
2 cm20 mm <br />0.02 m <br /> (30 cm300 mm <br />0.3 m <br />) +
reduced +
free +  and distinct +
open to congested +
Calif. +  and Oreg. +
not +  and aggregated +
0.2 cm2 mm <br />0.002 m <br /> (0.3 cm3 mm <br />0.003 m <br />) +
linear +  and lanceolate or narrowly elliptic +
0.02 cm0.2 mm <br />2.0e-4 m <br /> (0.04 cm0.4 mm <br />4.0e-4 m <br />) +
0.04 cm0.4 mm <br />4.0e-4 m <br /> (0.08 cm0.8 mm <br />8.0e-4 m <br />) +
0.05 cm0.5 mm <br />5.0e-4 m <br /> (0.2 cm2 mm <br />0.002 m <br />) +
flattened +
0.01 cm0.1 mm <br />1.0e-4 m <br /> (0.04 cm0.4 mm <br />4.0e-4 m <br />) +
open to congested +
0.4 cm4 mm <br />0.004 m <br /> (1 cm10 mm <br />0.01 m <br />) +
unisexual +  and bisexual +
not +  and aggregated +
obliquely ovoid +  and reniform +
0.08 cm0.8 mm <br />8.0e-4 m <br /> (0.3 cm3 mm <br />0.003 m <br />) +
open to congested +
0.1 cm1 mm <br />0.001 m <br /> (0.3 cm3 mm <br />0.003 m <br />) +
0.1 cm1 mm <br />0.001 m <br /> (0.25 cm2.5 mm <br />0.0025 m <br />) +
pilose +  and glabrous +
0.1 cm1 mm <br />0.001 m <br /> (0.55 cm5.5 mm <br />0.0055 m <br />) +
crassinucellate +
opposite +  and alternate +
marcescent +
winter-persistent +
separate +  and slightly overlapping +
2 cm20 mm <br />0.02 m <br /> (3 cm30 mm <br />0.03 m <br />) +
0.7 cm7 mm <br />0.007 m <br /> (1 cm10 mm <br />0.01 m <br />) +
0.5 cm5 mm <br />0.005 m <br /> (2 cm20 mm <br />0.02 m <br />) +
divided +, elliptic +  and cuneate-oblong +
0.15 cm1.5 mm <br />0.0015 m <br /> (?) +  and 0.7 cm7 mm <br />0.007 m <br /> (?) +
linear +  and filiform +
palmate +  and pinnate +
shallowly toothed +  and deeply divided +
aromatic +
inferior +  and superior +
clustered +, biseriate +  and superposed +
0.6 cm6 mm <br />0.006 m <br /> (1 cm10 mm <br />0.01 m <br />) +
0.2 cm2 mm <br />0.002 m <br /> (0.6 cm6 mm <br />0.006 m <br />) +
0.4 cm4 mm <br />0.004 m <br /> (0.45 cm4.5 mm <br />0.0045 m <br />) +
0 (?) +  and 4 (?) +
free +  and distinct +
0.15 cm1.5 mm <br />0.0015 m <br /> (0.4 cm4 mm <br />0.004 m <br />) +
0.03 cm0.3 mm <br />3.0e-4 m <br /> (0.15 cm1.5 mm <br />0.0015 m <br />) +
adnate +, free +, connate +  and distinct +
in War Department [U.S.], Pacif. Railr. Rep. +
not arillate +
abaxially green +  and reddish +
persistent +
free +  and distinct +
obtuse +  and acute +
0.15 cm1.5 mm <br />0.0015 m <br /> (0.3 cm3 mm <br />0.003 m <br />) +
free +  and distinct +
branched +  and simple +
stramineous +, reddish +  and green +
decumbent +  and nearly erect +
1 +  and 10 +
palmate +  and pinnate +
0.3 cm3 mm <br />0.003 m <br /> (1.2 cm12 mm <br />0.012 m <br />) +
deciduous +
distinct +
subterminal +
filiform +
rough-thickened +
0.1 cm1 mm <br />0.001 m <br /> (0.25 cm2.5 mm <br />0.0025 m <br />) +
Ambiguae +, Hirsutae +, Horkelia sect. Hirsutae +, Sericatae +  and Horkelia sect. Sericatae +
Horkelia tridentata +
Horkelia sect. Tridentatae +
species +
triangular +
1 cm10 mm <br />0.01 m <br /> (?) +
inconspicuous +
enlarged +
plant +  and rosette-forming +
hairy +  and inconspicuously conspicuously glandular +