Brittonia 33: 165, fig. 1. 1981.
Plants grayish, ± matted. Stems ± prostrate, 0.4–1.5 (–2) dm. Basal leaves tightly cylindric, (1.5–) 2–5 (–7) cm; sheathing base densely hairy abaxially; petiole 0.5–4 cm; lateral leaflets (5–) 8–15 per side, overlapping at least distally, ± flabellate, 0.5–2 mm, incised to base or nearly so into (0–) 3–8 (–15) elliptic to narrowly obovate lobes, apex not or obscurely setose, surfaces densely hirsute, cryptically glandular; terminal leaflets indistinct. Cauline leaves (0–) 1; blade reduced. Inflorescences 20–200-flowered, congested, (1–) 1.5–6 (–10) cm diam. Pedicels 1.5–6 mm. Flowers 4–6 mm diam.; epicalyx bractlets 5, lanceolate to elliptic, 0.6–1.5 (–2) mm; hypanthium shallowly cupulate, 1 × 2–3 mm; sepals (1–) 1.5–2.5 (–3) mm, acute; petals white to pale yellowish, linear, 1 mm; stamens 5, filaments 0.3–1 mm, anthers yellow with maroon margins, ovate, 0.3–0.5 mm; carpels 1–2 (–3), styles 0.7–1.8 mm. Achenes brown, 0.8–1.5 mm, smooth, prominently carunculate.
Phenology: Flowering summer.
Habitat: Dry shallow volcanic ash and cinders atop volcanic bedrock, open sagebrush communities, adjacent conifer woodlands
Elevation: 1500–1800 m
Of conservation concern.
Ivesia paniculata is known only from the Ash Valley area of Lassen County. The distinctions between I. paniculata and I. rhypara are perhaps on the same scale as variation among disjunct population clusters of I. rhypara, but no taxonomic adjustments are proposed at this time.
"dm" is not declared as a valid unit of measurement for this property.