Collomia is a genus of 16 species of annual or perennial herbs native to western North America and southern South America. One species, C. linearis, is particularly widespread in North America. Because of its ruderal habitat, the eastern edge of its range is uncertain but it is presumed to be introduced in northeastern North America, where it may be found as a waif along railroads.
Phylogeny
While the topology of Johnson et al. (2008) suggested that Collomia is a grade rather than a clade (viz. the placement of C. heterophylla), more recent work by Rose & Sytsma (2021) using a larger number of DNA markers recovered a monophyletic Collomia. In either case, the grade or clade of Collomia is sister to Navarretia (excluding N. sinistra). Molecular phylogenetic work by Leigh Johnson and colleagues (Johnson & Johnson 2006; Green 2010; Johnson et al. 2012; Johnson & Porter 2017) has done much to help elucidate the relationships in this genus, particularly C. linearis and its closest relatives. These DNA data suggest chloroplast capture by C. mazama from a relative of C. rawsoniana, as well as hybrid speciation leading to the formation of both C. wilkenii and C. biflora.
The phylogenetic trees to the left show relationships in some annual species of Collomia, particularly with regard to the origin of South American lineages (in grey) based on plastid (A) or three nuclear (B-D) markers. Trees are from Johnson & Porter (2017) and show a clear allopolyploid origin for C. biflora, evidenced by the occurence of cloned nuclear sequences in two distantly related clades.
Wherry (1944) recognized three sections within Collomia: Collomia (annuals with locules 1-seeded), Collomiastrum (perennials with locules 1-seeded), and Courtoisia (annuals with locules 2- or 3-seeded). Only sect. Courtoisia has presently held up with molecular data (Rose & Sytsma [2021]), with the current circumscription of sect. Collomia found in three clades and sect. Collomiastrum in two clades. One clade of sect. Collomia (C. tinctoria + C. tracyi) is sister to the rest of the genus and is supported by the trait of pantoporate pollen with radiate ridges (Type III pollen of Chuang et al. [1978]), perhaps justifying recognition of a new section. More DNA information is needed to clarify the sectional delimitation of the remaining members of sects. Collomia and Collomiastrum.
Biogeography
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, C. biflora, endemic to Argentina, Bolivia, and Chile, is an allotetraploid between C. grandiflora or C. soehrensii and C. linearis (Johnson & Johnson 2006; Johnson et al. 2012; Johnson & Porter 2017). 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.
Taxonomy
Collomia contains the following 16 species (* indicates South American species, evidence from Johnson et al. [2012] suggest that C. grandiflora also naturally occurs in South America).
- Collomia biflora (Ruiz & 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 soehrensii Phil.*
- 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…2
1′. Annual from a taproot; never caespitose…6
2. Corolla bright red; lobes acute, + 30 mm…C. rawsoniana
2′. Corolla violet to blue; lobes obtuse, 10–35 mm long…3
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
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
5. Stamens included…C. debilis subsp. trifida
5′. Stamens exserted…6
6. Some leaves 3–7 lobed…C. debilis subsp. debilis
6.’ Leaves entire or rarely 1–4 lobed…C. debilis subsp. camporum
7. Leaves conspicuously coarsely dentate…8
7′. Leaves entire or inconspicuously toothed…9
8. Calyx 5–8 mm long; corolla throat yellow; growing on or off serpentine…C. heterophylla
8′. Calyx 10–12 mm long; corolla throat purple; serpentine endemic…C. diversifolia
9. Stem with few or no lateral branches; inflorescence head-like…10
9′. Stem branched; flowers solitary or in small clusters…13
10. Corolla red, ca. 15 mm long; strictly South America…C. biflora (including C. cavanillesii)
10′. Corolla pink to salmon; 8–30 mm; North or South America…11
11. Corolla 15–30 mm long (except cleistogamous forms); tube much longer than calyx…12
11′. Corolla 8–15 mm long; tube little longer than calyx…C. linearis
12. Flowers approach herkogamous; style and anthers included; stamens + equal; South America…C. soehrensii
12.’ Flowers reverse herkogamous; styles exserted; stamens unqueal; mostly North America…C. grandiflora
13. Calyx 8–9 mm long, little exceeded by corolla…14
13′. Calyx 4–8 mm long, much exceeded by corolla…15
14. Plants eglandular…C. renacta
14′. Plants glandular…C. macrocalyx
15. Corolla 4–6 mm long…C. tenella
15′. Corolla 8–25 mm long…16
16. Corolla 8–14 mm long; stamens equally inserted in the corolla tube…C. tinctoria
16′. Corolla 9–22 mm; stamens unequally inserted in the corolla tube…17
17. Corolla (7–)9–10 mm long…C. wilkenii
17′. Corolla 12–22 mm long…C. tracyi
References
Chuang, T. I., Hsieh, W. C., & Wilken, D. H. (1978). Contribution of pollen morphology to systematics of Collomia (Polemoniaceae). American Journal of Botany, 65(4), 450-458.
Grant, V. (1959). Natural history of the phlox family. Vol. 1. Systematic botany. Natural history of the phlox family. Vol. 1. Systematic botany.
Green, E. S. (2010). Infrageneric relationships within Collomia (Polemoniaceae). M.S. Thesis. Brigham Young University.
Johnson, L. A., Chan, L. M., Weese, T. L., Busby, L. D., & McMurry, S. (2008). Nuclear and cpDNA sequences combined provide strong inference of higher phylogenetic relationships in the phlox family (Polemoniaceae). Molecular Phylogenetics and Evolution, 48(3), 997-1012.
Johnson, L. A., Chan, L. M., Pozner, R., & Glazier, L. D. (2012). Allotetraploids in Patagonia with affinities to western North American diploids: Did dispersal or genome doubling occur first? The Botanical Review, 78, 288-306.
Johnson, L. A., & Johnson, R. L. (2006). Morphological delimitation and molecular evidence for allopolyploidy in Collomia wilkenii (Polemoniaceae), a new species from northern Nevada. Systematic Botany, 31(2), 349-360.
Johnson, L. A., & Porter, J. M. (2017). Fates of angiosperm species following long‐distance dispersal: Examples from American amphitropical Polemoniaceae. American Journal of Botany, 104(11), 1729-1744.
Rose, J. P., & Sytsma, K. J. (2021). Complex interactions underlie the correlated evolution of floral traits and their association with pollinators in a clade with diverse pollination systems. Evolution, 75(6), 1431-1449.
Wherry, E. T. (1944). Review of the genera Collomia and Gymnosteris. The American Midland Naturalist, 31(1), 216-231.
Evolution of the Phlox Family 