Plants to 80 cm tall. Stems unarmed; twigs tomentose. Primary leaves narrowly oblanceolate, 1–2 cm long, tomentose; fascicled leaves smaller. Inflorescence heads terminating branches in a corymbiform array. Involucre 7–10 mm high; phyllaries 4, tomentose. Disk corollas 7–12 mm long. Achenes 3–5 mm long glabrous or sericeous (
Lesica et al. 2012. Manual of Montana Vascular Plants. BRIT Press. Fort Worth, TX).
Montana has 2
Tetradymia species:
Gray Horsebrush -
Tetradymia canescens *Stems: Unarmed.
*Flower Heads: Grow in clusters (corymbiform) at tips of stems.
Short-spine Horsebrush -
Tetradymia spinosa, SOC
*Stems: Spiny.
*Flower Heads: Grow from leaf axils.
Possible look-alikes include yellow-flowered shrubs in the Sunflower (Asteraceae) Family:
Tetradymia - Horsebrush
*Flower Heads: Ray florets are absent
and pappus is of capillary bristles.
*Twigs: White-tomentose (hairy) with or without spines
andUpper Leaves are fascicled.
Artemisia - Sagebrush
*Flower Heads: Arranged in a raceme or panicle, involucral bracts in 4-7 unequal rows,
and pappus is absent.
*Leaves: Usually lobed, but some species with simple leaves.
Ericameria - Goldenbrush / Rabbitbrush
*Flower Heads: a) Ray florets are absent
and pappus is of capillary bristles, or b) Some ray florets are present.
*Twigs: a) White-tomentose (hairy) without spines
and upper Llaves are mostly not fascicled, or b) glabrous and greenish.
Chrysothamnus - Rabbitbrush
*Flower Heads: Ray florets are absent
and pappus is of capillary bristles.
*Twigs: Glabrate to puberulent
and leaves are resin-dotted.
Gutierrezia sarothrae - Broom Snakeweed
*Flower Heads: Arranged in flat-topped clusters (corymbiform), ray florets present,
and pappus is of jagged (erose) scales.
*Plants are short, often less than 30 cm tall.
Lorandersonia linifolia - Spearleaf Rabbitbrush, PSOC
*Flower Heads: Ray florets are absent
and pappus is of capillary bristles.
*Twigs: Mostly without hairs (glabrous), has a whitish epidermis,
and leaves lack glands.
