Collomia is a genus of 15 species of annual or perennial herbs native to western North America and southern South America. One species, Collomia linearis, may be found as a waif along railroads in northeastern North America.
Collomia may or may not be monophyletic as the position of C. heterophylla in Johnson et al. (2008) suggests that the genus is a grade rather than a clade. However, my unpublished data suggests that C. heterophylla is part of the earliest diverging clade of a monophyletic Collomia. In either event, the grade or clade of Collomia is sister to Navarretia. The thesis work of Green (2010) and work by Johnson et al. (2012) has done much to help elucidate the relationships in this genus which has suggested chloroplast capture by C. mazama from a relative of C. rawsoniana, as well as hybrid speciation leading to the formation of C. wilkenii and C. biflora.
Collomia is native the both the western United States and South America. Collomia linearis is occasionally found as a waif along railroad tracks in the eastern United States, but is here only considered native as far east as North Dakota. While most species of Collomia occur in western North America and are diploid, one is found in Patagonia and is tetraploid. Grant (1959) suggested that all southern hemisphere Polemoniaceae arrived there via a long distance dispersal event during the Pleistocene, likely with their mucilaginous seeds attached to the feet of shorebirds.
Collomia contains the following 16 species (* indicates South American species, evidence from Johnson et al. (2012) suggest that C. grandiflora or may also naturally occur in South America):
- Collomia biflora (Ruiz and Pav.) Brand*
- Collomia debilis (S. Wats.) Greene
- Collomia debilis (S. Wats.) Greene subsp. camporum Pays.
- Collomia debilis (S. Wats.) Greene subsp. debilis
- Collomia debilis (S. Wats.) Greene subsp. trifida Pays.
- Collomia diversifolia Greene
- Collomia grandiflora Douglas
- Collomia heterophylla Douglas
- Collomia larsenii (A. Gray) Pays.
- Collomia linearis Nutt.
- Collomia macrocalyx Leiberg
- Collomia mazama Coville
- Collomia rawsoniana Greene
- Collomia renacta Joyal
- Collomia tenella A. Gray
- Collomia tinctoria Kell.
- Collomia tracyi H. Mason
- Collomia wilkenii L.A. Johnson & R.A. Johnson
KEY TO COLLOMIA (modified from Wherry (1944))
1. Caespitose, rhizomatous perennial; seeds not mucilaginous when wet
2. Corolla bright red; lobes acute, + 30 mm…C. rawsoniana
2′. Corolla violet to blue, lobes obtuse, 10-35 mm
3. Plants erect, distinctly caulescent; flowers blue; Crater Lake OR…C. mazama
3′. Plants compact, depressed; flowers dull pink to dull violet, more widespread
4. Leaves deeply ternately lobed; calyx 5-9 mm…C. larsenii
4′. Leaves entire or shallowly pinnately lobed; calyx 8-10 mm (C. debilis)
5. Stamens included…C. d. trifida
5′. Stamens exserted…C. d. debilis
1′. Plants annual from a taproot; never caespitose; seeds mucilaginous when wet
6. Leaves conspicuously coarsely dentate
7. Calyx 5-8 mm…C. heterophylla
7′. Calyx 10-12 mm…C. diversifolia
6′. Leaves entire or inconspicuously toothed
8. Stem with few or no lateral branches, inflorescence head-like
9. Corolla red; South America…C. biflora
9′. Corola pink to salmon; N. America (C. grandiflora rarely escapes in S. America)
10. Corolla 15-30 mm (except in cleistogamous forms); tube much longer than calyx…C. grandiflora
10′. Corolla 8-15 mm; tube little longer than calyx…C. linearis
8′. Stem branched; flowers solitary or in small clusters
11. Calyx 8-9 mm long; little exceeded by corolla
12. Plants egandular…C. renacta
12.’ Plants glandular…C. macrocalyx
11′. Calyx 4-8 mm long; much exceeded by corolla
13. Corolla 8-25 mm
14. Corolla 8-14 mm; stamens equally inserted…C. tinctoria
14′. Corolla 9–22 mm; stamens unequally inserted
15. Corolla (7-) 9-10 mm long…C. wilkenii
15′. Corolla 12–22 mm…C. tracyi
13′. Corolla 4-6 mm…C. tenella