Osmadenia Nutt.

Last Addition: November 25, 2006.  Each "thumbnail" image below is linked to a larger photograph.

Osmadenia is an aromatic, monotypic annual genus extending from southern California into Baja, Mexico.  It is closely related to Calycadenia, but lacks the tack-shaped glands characteristic of that genus.  Plants 0.5 - 4 dm tall.  Leaves alternate, reduced above.  Heads radiate, phyllaries 3 - 5, each partly enfolding a ray ovary; ray florets pistillate, the corolla limb deeply 3-lobed, white to reddish, sometimes red-spotted; receptacular chaff peripheral and fused into a cup-like false involucre; disk florets 3-10, perfect, the corolla color similar to rays, the anthers yellow;  cypselae dimorphic, those of the ray florets epappose, thick-walled, with inner face more or less flat, outer face rounded to angled, those of the disk florets with pappus of about 8 alternating long and short scales, thin-walled, angled, tapered at base.  The chromosome number is n = 9.  Intergeneric hybrids combining Osmadenia with each of three different species of Calycadenia at n = 7 have been synthesized experimentally.

O. tenella. 1-3 --  Plant in habitat in San Diego County, CA.  4 --  Plant in cultivation.  5 -- Capitulum, note red blotches on lateral lobes of ray corollas and on lobes of disk florets. 6 -- Capitulum, red blotches absent on ray corollas. 7 -- Ray and disk florets.

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