|Flaxleaf Whitetop Aster (Ionactis linariifolia)|
The generic name, Ionactis, is derived from two Greek words meaning "violet rays."
This aster-like plants are endemic in North America. Four species occur on dry clearings or rocky slopes at mid to high elevations in the Rocky Mountains and the Cascade Mountains. One species, Ionactis linariifolia, occurs in most of eastern North America.
Ionactis was classified as a separate genus by Edward Lee Greene in 1897 with the species Ionactis linariifolia, which had been classified by Carolus Linnaeus as Aster linariifolius. Three other species were formerly classified under Aster, Chaetopappa or Ionactis. The species of Aster (in a strict sense) are now restricted to Eurasia.
The Stiff-leaved Asters are perennial herbs with numerous green stems, about 2,5 cm long (rarely 10 cm), usually in a tussock. The spatulate leaves are small, stiff, sharply ascending and thick about the stem. The upper leaves are much smaller than the lower. Yellow-orange resin droplets form on the leaves of the Red Rock Canyon Aster (Ionactis caelestis).
The involucral phyllaries (bracts under the flower head) are narrow and overlapping. They have, along the midrib, a narrow zone containing chlorophyll. The silky-hairy, fusiform achenes form a crown with a double pappus in two series, the inner one with long, barbellate bristles, the outher one with short bristles or minute scales.
The small flower heads grow solitary or sometimes in a cluster at the end of the stems. The 10–24 fertile ray florets are nearly white, blue to pink, lavender, purple or blue violet. The sterile disc florets are yellowish. The peduncles are nearly naked.
They have a chromosome base number of x = 9.
- Ionactis alpina : Lava Aster, Alpine Ionactis.
- Ionactis caelestis : Red Rock Canyon Aster, described in 1992 by P. J. Leary and Guy L. Nesom.
- Ionactis elegans : Sierra Blanca Cliff Daisy.
- Ionactis linariifolia : Flaxleaf Whitetop Aster, Grass-leaf Aster, Narrow-leaved White-topped Aster.
- Ionactis stenomeres : Rocky Mountain Aster.
- Nesom, G. 1994. - Review of the taxonomy of Aster sensu lato (Asteraceae: Astereae), emphasizing the new world species. Phytologia 77:141-297.
- Xiang, C. & J.C. Semple. 1996. - Molecular systematic study of Aster sensu lato and related genera (Asteraceae: Astereae) based on choroplast DNA restriction site analyses and mainly North American taxa. Pp. 393-423, in D.J.N. Hind & H.J. Beentje (eds.), Compositae: systematics. Proc. Intern.