Silphium perplexum J.R. Allison

Old Cahaba Rosinweed

Herb

Perennial

Vascular

Old Cahaba Rosinweed is a native herbaceous perennial in the Aster family (Asteraceae). It is an Alabama endemic, known from three counties in west central Alabama. All known populations are located within nine miles of the Cahaba River. Old Cahaba Rosinweed is a perennial from a short rhizome. Basal leaves are usually absent at flowering. The stems are from one to eight feet in height, and are unbranched below the inflorescence. Stem leaves are lanceolate or ovate, opposite, and sessile or with short winged petioles. The leaf bases clasp the stem. The leaf margins may be entire or with a few teeth. The stems, leaves, and phyllaries are pubescent and glandular. The glands are stalked and amber colored. The entire plant has a resinous feel. Flowers are produced in heads. The heads are arranged in open panicles. Each plant may have from one to thirty heads. Ray and disc flowers are bright yellow. Rays average 19-23 per head. The fruit is an achene. Old Cahaba Rosinweed is similar to another Alabama endemic-- Sticky Rosinweed (Silphium glutinosum J.R. Allison). That species is known only from Bibb County. It is a shorter plant with fewer ray flowers and longer stalked glands. Old Cahaba Rosinweed is postulated to have arisen from hybridization between Sticky Rosinweed and Entire Leaf Rosinweed (Silphium integrifolium Michaux) as it is intermediate in most characteristics between those two species. Old Cahaba Rosinweed is listed as an S1 species in Alabama (typically 5 or fewer occurrences, very few remaining individuals, acres, or miles of stream, or some factor of its biology making it especially vulnerable in the state), and globally as a G1 species (critically imperiled globally because of extreme rarity (5 or fewer occurrences), or very few remaining acres, or miles of stream) or especially vulnerable to extinction because of some factor of its biology).--A. Diamond

**

Native Endemic S1 (State Rank) G1 (Global Rank)

**