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We saw this plant frequently during our 2 Jepson workshop days in the SSPM...it was identified for us as Ipomopsis effusa by Jon Rebman. The remarks for this species in the 2010 annotated plant list by Thorne, Moran & Minnich are:
''Common annual of open pine forest, sandy-gravelly flats, and moist stream bottoms, 1600–2500 m. Largely restricted to Sierra Juarez and SSPM, but reported also from Pinto Wash, Imperial Co., CA''
More images of Ipomopsis effusa can be found on the SDMNH photo page (search under the species name there), and at this SEINET link.
This species does not seem to key correctly in Wiggins' 1980 'Flora of Baja California', due to its conspicuously irregular (bilateral) corolla. An abbreviated version of Wiggins' keying sequence for Ipomopsis is:
Leaves alternate; stems leafy, not scapose; calyces regular; corollas regular; flowers not in heads.
It does key correctly to Ipomopsis in the JM2 Polemoniaceae key and to species I. effusa in the JM2 Ipomopsis key. Although the species is considered endemic to Baja, it still appears the the JM2 due to the record from Imperial Co. mentioned above, which is thought to have been a waif washed down from the Sierra Juarez in Baja.
I was curious as to the details of how this came to be placed in the genus Ipomopsis? The gestalt of the flowers seemed closer to a Loeseliastrum to my eye.
Indeed, researching on the web I found that the taxon was originally described as Loeselia effusa by Asa Gray in 1876 (holotype image here). Later it was variously treated as Navarretia effusa Kuntze 1891 and Gilia effusa J.F.Macbr. 1918, before being moved to Ipomopsis effusa by Moran in 1977.
I couldn't gain access to Moran's 1977 Madroño paper, but two recent papers addressing my question are cited below:
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: 853–861. (Full Text)
J. M. Porter, L. A. Johnson, and D. Wilken. (2010). Phylogenetic Systematics of Ipomopsis (Polemoniaceae): Relationships and Divergence Times Estimated from Chloroplast and Nuclear DNA Sequences. Systematic Botany, 35(1): pp. 181–200 (Full Text)
The first paper is somewhat intelligible to me and is very interesting as it seems to give a substantial argument supporting caution in treating molecular data as the principal basis for taxonomic arrangements. The second paper is mostly too technico-molecular-cladistic for me to genuinely understand or digest (given my current knowledge of molecular taxonomy), and the conclusions regarding taxonomic relationships there seem rather confusing to me.