Phacelia crenulata, heliotrope phacelia
Fig. 1. Phacelia crenulata, heliotrope phacelia. Top row: Inflorescence branch of var. ambigua on the left; var. minutiflora on the right.
Middle and bottom rows. Left: var. ambigua. Right: var. minutiflora.
The difference in flower size is very apparent when these two varieties are seen side by side, or in photographs that show the entire plant. However, the flowers look very similar is close-ups that have no scale. In the middle row, note how showy var. ambigua is compared to var. minutiflora, even though both plants are in full bloom. In the bottom row, note that both varieties have a white throat. Click on the bottom four pictures for larger versions.
Note that the flower color depends strongly on lighting and how one processes the picture. The top photograph was taken inside by flash on white paper; the other photographs were taken in the field. See another version of the top photograph taken inside without using flash on manila paper, for dramatically-different colors! (Note that the varieties are on different sides in the linked photograph.)
Table of Contents
Phacelia crenulata is the most common phacelia species of the Borrego Desert Floor (P. distans is the most common phacelia species west of the Borrego Desert Floor). It has a number of common names: heliotrope phacelia, cleftleaf wildheliotrope, and notch-leaved phacelia. In addition to these common names, its large-flowered variety ambigua is sometimes called purplestem phacelia, and its small-flowered variety minutiflora is sometimes called little-flowered heliotrope phacelia.
There has been, and still is, considerable confusion about how to distinguish these two varieties since the keys in floras to distinguish them have problems; see Comments on the 1993 Jepson Manual First Edition.
As an example of the difficulties in determining vouchers, in Beauchamp's 1986 Flora of San Diego County, var. minutiflora was considered to be scarce in San Diego County, with only two locations given, with var. ambigua considered to be occasional, with 13 locations given. In contrast, we have more records of var. minutiflora in our database compared to var. ambigua, 25 vs. 16, and there are now more vouchers of var. minutiflora from San Diego County compared to var. ambigua, 45 vs. 39. It appears that at least some of the vouchers examined by Beauchamp have had their determinations changed after 1986 from var. ambigua to var. minutiflora, since some of the locations listed by Beauchamp for var. ambigua now have only vouchers determined as var. minutiflora.
Part of the difficulty in making a key is having to include var. crenulata, which we don't have in the Borrego Desert, which makes even the current Jepson eflora key misleading in how to separate the species based on corolla size and corolla throat color.
Our two varieties are easy to distinguish almost at a glance based on how showy the flowers are, since the flowers of var. minutiflora are much smaller than those of var. ambigua. We will try to quantify the size of the flowers in the future, since the measurements given in the floras are not accurate for our plants. Var. ambigua sometimes has clearly much-more-exserted stamens than var. minutiflora, but that is not always the case.
This page primarily exists now as a placeholder for the geographic distribution of this species.
The known geographic distribution of the two varieties of Phacelia crenulata, from accurate GPS observations in the field and from vouchers with localities that are accurate to less than a half mile, is shown in Fig. 2.
Fig. 2. The geographic distribution of Phacelia crenulata in the Borrego Desert area, from our GPS records and from vouchers with well-defined localities. Left: var. ambigua. Right: var minutiflora. Click on the maps for larger versions.
Fig. 3 shows the two species on the same map.
Fig. 3. The geographic distribution of both varieties of P. crenulata, both from our digitized GPS records and from vouchers with well-defined localities. This map corresponds in area closely to the area shown in Fig. 2; see those maps for landmarks. Note the nearly-complete, but not absolute, geographic separation of the varieties.
These two varieties have an almost completely-disjunct distribution in the Borrego Desert, even though both varieties are found together in a number of other areas of California (see southern California voucher maps for var. ambigua and for var. minutiflora).
The western and southern portion of the Borrego Desert contains almost entirely var. minutiflora, except for a single voucher of var. ambigua, SDSU6085. We've asked Mike Simpson to recheck the determination of that voucher.
The northeastern portion of the Borrego Desert contains almost entirely var. ambigua, except for a very small number of records for var. minutiflora. One of those records is the plant shown in Fig. 1, that was found at the parking area for Palm Wash. There are hundreds of plants of var. ambigua that we've seen in the general area, so it is possible that this single record of var. minutiflora was a waif. Our other two records in that area were of a single plant, and of three plants, so even if these plants are not waifs, var. minutiflora is clearly not very abundant in this area that is dominated heavily by var. ambigua.
Our records give an elevation range from 530 to 1060 feet for var. ambigua, and from 430 to 1730 feet for var. minutiflora. Voucher elevations range from zero to 1000 feet for var. ambigua, and from 60 to 2020 feet for var. minutiflora. (Vouchers with stated elevations above 1000 feet for var. ambigua either have elevations inconsistent with their localities, or are almost certainly misdetermined.)
Combining our records with vouchers, var. ambigua ranges from zero to 1060 feet elevation in our area, and var. minutiflora ranges from 60 to 2020 feet.
Voucher data provided by the participants of the Consortium of California Herbaria (ucjeps.berkeley.edu/consortium/) on 12 February 2016.
Copyright © 2016 by Tom Chester, Mike Crouse, Kate Harper, Adrienne Ballwey, and James Dillane.
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Comments and feedback: Tom Chester
Updated 13 February 2016