Ipomopsis

Ipomopsis is a taxonomically complex genus of 28 species native to North America and South America. Ipomopsis aggregata (scarlet gilia) and I. rubra (standing cypress) are perhaps the best known species. Ipomopsis aggregata has received considerable attention from pollination biologists studying selection on floral traits on short evolutionary time scales. However, it is by far and most taxonomically complex species in the genus, with at least nine subspecies and possibly more if it is expanded to include variation currently recognized as I. tenuituba.

Phylogeny

Molecular phylogenetic evidence from Porter et al. (2010) clearly demonstrated that Ipomopsis was not monophyletic with I. havardii and I. sonorae being most closely related to Dayia, These species have since been transferred to that genus. Ipomopsis is sister to the monotypic Bryantiella (B. palmeri). There are three major clades within Ipomopsis. Zygomorphic-flowered species from Baja California (I. effusa, I. guttata, I. tenuiflora) form sect. Giliopsis which is in turn sister to the other two sections. Section Giliopsis has been studied in detail by Wood & Nakazato (2009) and Nakazato et al. (2013). The rest of Ipomopsis forms two well-supported clades corresponding to taxonomic sections. (1) A clade of white or cream-flowered annuals or long-lived perennials with short corolla tubes (sect. Elaphocera) and (2) a clade of mostly hummingbird or lepidopteran-pollinated biennial or short-lived perennial plants with long corolla tubes (sect. Ipomopsis). A single species (I. polycladon) is morphologically similar to sect. Elaphocera but is sister to sect. Ipomopsis. Porter et al. (2010) treated it as incertae sedis but may warrant recognition as a monotypic section. Within sections, monophyly of species is generally well-supported but relationships between species are poorly supported (Porter et al. 2010; Rose & Sytsma 2021). This is probably part due in part to discordance between the plastid and nuclear genomes (Porter et al. 2010).

Porter et al. (2010) estimated a divergence time of 36.64 + 0.31 mya for the crown of Ipomopsis and a divergence time of 15.97 + 0.25 mya for the I. aggregata species complex. However, Rose & Sytsma (2021) using different methods for divergence time estimation and different placement of fossils estimated more recent divergence times of 26.92 and 8.71 mya, respectively.

Biogeography

Ipomopsis is largely native to arid and high-elevation areas of the Great Plains and western North America.  One species, I. rubra extends into eastern North America along the Coastal Plain, where is probably only native from Texas to North Carolina (Sorrie et al. 2018). One annual species, I. gossypifera, is native to South America (Johnson and Porter 2017). It is estimated to diverged from its closest relative in North America, I. pumila, 4.58 mya. However, dispersal to South America could have occurred more recently.

Taxonomy (* indicates South American taxa)

As mentioned above, Ipomopsis is a taxonomically complex genus. This is clearly evidenced by the large number of subspecific entities listed below.  Much of the nomenclatural complexity is likely a result of multiple factors including elevational ecotypes and hybrid swarms (Grant and Wilken 1987, 1988). The I. aggregata complex has been treated by Grant and Wilken (1986), the I. congesta complex by several authors (Constance & Rollins 1936; Day 1980; Porter 2011), the I. spicata complex by Wilken and Hartman (1991), and the I. multiflora/polyantha complex by Wilken (2019). A robust hypothesis of phylogenetic relationships in the genus is desperately needed to help rectify these and other taxonomic issues.

1. Ipomopsis aggregata (Pursh) V.E. Grant
   • I. aggregata (Pursh) V.E. Grant subsp. aggregata
   • I. aggregata (Pursh) V.E. Grant subsp. attenuata (A.Gray) V.E. Grant & A.D. Grant
   • I. aggregata (Pursh) V.E. Grant subsp. bridgesii (A. Gray) V.E. Grant & A.D. Grant
   • I. aggregata (Pursh) V.E. Grant subsp. candida (Rydb.) V.E. Grant & A.D. Grant
   • I. aggregata (Pursh) V.E. Grant subsp. carmenensis Henr.
   • I. aggregata (Pursh) V.E. Grant subsp. collina (Greene) Wilken & Allard
   • I. aggregata (Pursh) V.E. Grant subsp. formosissima (Greene) Wherry
   • I. aggregata (Pursh) V.E. Grant subsp. texana (Greene) Wherry
   • I. aggregata (Pursh) V.E. Grant subsp. weberi V.E. Grant & Wilken
2. Ipomopsis arizonica (Greene) Wherry
3. Ipomopsis congesta (Hook.) V.E. Grant
   • I. congesta (Hook.) V.E. Grant subsp. congesta
   • I. congesta (Hook.) V.E. Grant subsp. crebrifolia (Nutt.) A.G. Day
   • I. congesta (Hook.) V.E. Grant subsp. frutescens (Rydb.) A.G. Day
   • I. congesta (Hook.) V.E. Grant var. goodrichii Welsh
   • I. congesta (Hook.) V.E. Grant subsp. mathewii J.M. Porter
   • I. congesta (Hook.) V.E. Grant subsp. montana (A. Nels. & P.B. Kenn.) V.E. Grant
   • I. congesta (Hook.) V.E. Grant subsp. nevadensis (Tidestr.) Karst. & Gandhi
   • I. congesta (Hook.) V.E. Grant var. ochroleuca Welsh
   • I. congesta (Hook.) V.E. Grant subsp. palmifrons (Brand) A.G. Day
   • I. congesta (Hook.) V.E. Grant subsp. pseudotypica (Constance & Rollins) A.G. Day
   • I. congesta (Hook.) V.E. Grant subsp. viridis (Cronq.) A.G. Day
4. Ipomopsis effusa (A. Gray) Moran
5. Ipomopsis gossypifera (Gillies) V.E. Grant*
6. Ipomopsis gunnisonii (Torr. & A. Gray) V.E. Grant
7. Ipomopsis guttata (A. Gray) Moran
8. Ipomopsis laxiflora (J.M. Coult.) V.E. Grant
9. Ipomopsis longiflora (Torr.) V.E. Grant
   • I. longiflora (Torr.) V.E. Grant subsp. australis R.A. Fletcher & W.L. Wagner
   • I. longiflora (Torr.) V.E. Grant subsp. longiflora 
   • I. longiflora (Torr.) V.E. Grant subsp. neomexicana Wilken
10. Ipomopsis macombii (Torr.) V.E. Grant
11. Ipomopsis macrosiphon (Kearney & Peebles) V.E. Grant & Wilken
12. Ipomopsis monticola J.M. Porter & L.A. Johnson
13. Ipomopsis multiflora (Nutt.) V.E. Grant
    • I. multiflora (Nutt.) V.E. Grant subsp. brachysiphon (Wooton & Standly) Wilken
    • I. multiflora (Nutt.) V.E. Grant subsp. multiflora
    • I. multiflora (Nutt.) V.E. Grant subsp. whitingii (Kearney & Peebles) Wilken
14. Ipomopsis pinnata (Cav.) V.E. Grant
15. Ipomopsis polyantha (Rydb.) V.E. Grant
16. Ipomopsis polycladon (Torr.) V.E. Grant
17. Ipomopsis pringlei (A. Gray) Henr.
18. Ipomopsis pumila (Nutt.) V.E. Grant
19. Ipomopsis ramosa A.L. Schneid. & Bregar
20. Ipomopsis roseata (Rydb.) V.E. Grant
21. Ipomopsis rubra (L.) Wherry
22. Ipomopsis sancti-spiritus Wilken & R.A. Fletcher
23. Ipomopsis spicata (Nutt.) V.E. Grant
    • I. spicata (Nutt.) V.E. Grant subsp. capitata (A. Gray) V.E. Grant
    • I. spicata (Nutt.) V.E. Grant subsp. orchidacea (Brand) Wilken & R.L. Hartm.
    • I. spicata (Nutt.) V.E. Grant subsp. robruthiae Wilken & R.L. Hartm.
    • I. spicata (Nutt.) V.E. Grant subsp. tridactyla Wilken & R.L. Hartm.
24. Ipomopsis tenuifolia (A. Gray) V.E. Grant
25. Ipomopsis tenuituba  (Rydb.) V.E. Grant
    • I. tenuituba (Rydb.) V.E. Grant subsp. latiloba V.E. Grant & Wilken
    • I. tenuituba (Rydb.) V.E. Grant subsp. tenuituba
26. Ipomopsis thurberi (Torr.) V.E. Grant
27. Ipomopsis wendtii Henr.
28. Ipomopsis wrightii (A. Gray) Shinners

References

Constance, L., & Rollins, R. C. (1936). A revision of Gilia congesta and its allies. American Journal of Botany, 23(6), 433-440.

Day, A. G. (1980). Nomenclatural changes in Ipomopsis congesta (Polemoniaceae). Madroño, 27(2), 111-112.

Grant, V., & Wilken, D. H. (1988). Natural hybridization between Ipomopsis aggregata and I. tenuituba (Polemoniaceae). Botanical Gazette, 149(2), 213-221.

Grant, V., & Wilken, D. H. (1987). Secondary intergradation between Ipomopsis aggregata candida and I. a. collina (Polemoniaceae) in Colorado. Botanical Gazette, 148(3), 372-378.

Grant, V., & Wilken, D. H. (1986). Taxonomy of the Ipomopsis aggregata group (Polemoniaceae). Botanical Gazette, 147(3), 359-371.

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.

Nakazato, T., Rieseberg, L. H., & Wood, T. E. (2013). The genetic basis of speciation in the Giliopsis lineage of Ipomopsis (Polemoniaceae). Heredity, 111(3), 227-237.

Porter, J. M. (2011). Two new Aliciella species and a new subspecies in Ipomopsis (Polemoniaceae) from the western United States of America. Phytotaxa, 15, 15-25.

Porter, J. M., Johnson, L. A., & Wilken, D. (2010). Phylogenetic systematics of Ipomopsis (Polemoniaceae): relationships and divergence times estimated from chloroplast and nuclear DNA sequences. Systematic Botany, 35(1), 181-200.

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.

Sorrie, B.A., Weakley, A. S., & Bradley, K.A. (2018). Ipomopsis rubra (Polemoniaceae): Distribution and habitat. Phytoneuron 2018-29: 1–8.

Wilken, D. H. (2019). Reassessment and circumscription of Ipomopsis multiflora and Ipomopsis polyantha (Polemoniaceae). Madroño, 66(3), 87-91.

Wilken, D., & Hartman, R. L. (1991). A revision of the Ipomopsis spicata complex (Polemoniaceae). Systematic Botany, 16, 143-161.

Wood, T. E., & Nakazato, T. (2009). Investigating species boundaries in the Giliopsis group of Ipomopsis (Polemoniaceae): strong discordance among molecular and morphological markers. American Journal of Botany, 96(4), 853-861.