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Silphium (Silphion the ancient Greek)

(Silphion, the ancient Greek name used by Hippocrates for a plant which produced some gum-resin, perhaps asafoetida, and which was transferred by Linnaeus to this genus). Rosin-plant. ORD. Compositae. A genus consisting of eleven species of tall, coarse, hardy, perennial herbs, with a copious resinous juice, confined to North America. Flower-heads yellow, large, corymbose-panicled; involucre broad and rather flat the scales imbricated in many rows; ray florets numerous, fertile; disk florets sterile; achenes glabrous, surrounded by a wing, which is notched at the top. Leaves alternate, opposite, or whorled, entire, toothed, or lobed. The best-known species are described below. Dr. Asa Gray says of S. laciniatum: "On the wide, open prairies the leaves are said to present their faces uniformly north and south, whence it is called the Compass-plant"; this peculiarity, according to other authorities, is more noticeable in young specimens. Any ordinary soil is suitable for the culture of these plants, which are best placed at the backs of flower-beds. They may be increased by division.

S. laciniatum (torn).* Compass Plant; Pilot Weed; Polar Plant. fl.-heads few, 1in. to 2in. broad, somewhat racemose; involucral scales rigidly pointed; achenes broadly winged. July. l. pinnatipartite, petioled but dilating and clasping at base, the lower and radical ones ovate, 1ft. to 2 1/2ft. long; divisions lanceolate or linear, acute, cut-lobed or pinnatifid, rarely entire. h. 3ft. to 6ft. Plant rough-bristly.(B. M. 6534.) S. perfoliatum (perfoliate-leaved). fl.-heads corymbose; achenes winged and variously notched. July. l. entire, ovate, 6in. to 15in. long, coarsely toothed, the upper ones united by their bases, and forming a cup-shaped disk, the lower ones abruptly narrowed into winged petioles, which are connate by their bases. Stem 4in. to 8in. high, square. (B. M. 3354.) S. terebinthinaceum (terebinthine). Prairie Dock. fl.-heads small; involucral scales roundish, obtuse, smooth; achenes narrowly-winged. July to September. l. ovate and ovate-oblong, somewhat cordate, serrate-toothed, rough, especially beneath, 1ft. to 2ft. long, on slender petioles. Stem smooth, 4ft. to 10ft. high, panicled at the summit, and bearing many heads. (B. M. 3525.) S. trifoliatum (three-leaved). fl.-heads loosely paniculate; achenes rather broadly winged. August. l., cauline ones lanceolate, pointed, entire or scarcely serrate, rough, short-petioled, in whorls of three or four, the uppermost ones opposite. Stem smooth, rather slender, 4ft. to 6ft. high, branched above, (B. M. 3355.)