Rhizomatous perennial. Stems erect, branched, 15–50 cm. Herbage glabrous. Leaves cauline, alternate, linear, 5–30 mm long; the upper reduced to scales. Heads ligulate, solitary on branch tips; involucre obconic, 9–16 mm high; phyllaries in 2 series; outer minute; inner ca. 5, linear, glabrous, scarious-margined; receptacle flat, naked. Ray flowers perfect, ca. 5; ligules 9–12 mm long, pinkish. Pappus off-white, capillary bristles. Achenes fusiform, 6–10 mm long, 5-ribbed, glabrous (
Lesica et al. 2012. Manual of Montana Vascular Plants. BRIT Press. Fort Worth, TX).
These plants can be confused by their common name, scientific name, and/or initial appearance because at some point they can exhibit green or brown stems that are leafless or inconspicuously leafy.
Here is how to differentiate them:
Rush Skeleton-plant -
Lygodesmia juncea, native:
* In Aster Family; pinkish flowerheads occur at the tips of stems. About 5 florets per flowerhead.
* Achenes are not beaked, but sometimes are fusiform.
* Plants lack milky sap.
* Plants are without hairs (glabrous).
* Plants are rhizomatous perennial forbs.
Rush skeletonweed -
Chondrilla juncea, exotic and Noxious:
* In Aster Family; yellow flowerheads occur at the tips of stems or in the axils of leaves. About 7-15 florets per flowerhead.
* Achenes (fruits) have a beak of 5-6mm long.
* Stems, leaves, and inflorescence have milky sap.
* Plants have hairs being hirsute to glabrate. On the lower 10-15 cm (4-6 inches) of the stem the hairs point downward while the upper stem is lacks hairs or has a few rigid hairs.
* Plants are taprooted perennial forbs.
Spiny Skeletonweed -
Pleiacanthus spinosus, native, SOC:
* In Aster Family; pinkish flowerheads occur solitary on upper branches. About 3 florets per flowerhead.
* Achenes are not beaked, but are tubular.
* Plants have a milky sap.
* Plants have hairs, being glabrate to weakly tomentose.
* Plants are taprooted with a brown-woolly branched crown.
* Stems are spine-tipped and branched.
Tall Tumble-mustard -
Sisymbrium altissimum, exotic:
* In Mustard Family; flowers with 4 (pale) yellow petals and 4 green to yellowish sepals.
* Stems are leafy with large pinnately lobed leaves.
* In fruit or during the winter stems appear leafless. Plants branch, becoming round.
* Fruit is a long and narrow silique that is equal in width to its stem (pedicel).
