Plant Species of San Jacinto Mountain:
Penstemon californicus, California penstemon
Bruce Watts and Tom Chester
Table of Contents
Fig. 1. Photographs of Penstemon californicus. From top to bottom: 1. Close-up of individual flowers. 2. A plant in glorious full bloom. 3. A handsome plant even without any blooms. 4. A young plant with perhaps its first blooms. 5. Some of the variation in flower color, from pinkish-purple flowers, to flowers with pink-purple centers and blue lobes, and pinkish flowers. Click on the pictures for larger versions. Photographs © Bruce Watts.
Penstemon californicus is one of those darling smallish plants found in Garner Valley and the Desert Divide at San Jacinto Mountain that is handsome even without its beautiful flowers; see Fig. 1. It is also an extremely rare species, being known in California only in three nearby places: Garner Valley, where most of the population is found; the Pacific Crest Trail in the vicinity of the Cedar Spring Trail; and the ridge east of Toro Peak in the Santa Rosa Mountains; see Fig. 2.
Outside of California, P. californicus is known from scattered locations in Baja California (Fig. 2). It wasn't common enough to be mentioned in the Baja California Plant Field Guide, Third Edition, Rebman and Roberts, 2012, which mentions three out of the 12 Penstemon species there.
The San Jacinto Mountain Garner Valley location is the northernmost population of this species, disjunct by something like 80 miles from the nearest population in Baja.
Due to its limited geographic range, P. californicus is listed by the California Native Plant Society (CNPS) as a "Rare Plant in California and elsewhere", and fairly endangered in California (CNPS List 1B.2).
P. californicus is a low mounded subshrub that grows in dry rocky areas. Typical plants are ~10 cm (4 inches) in height, and 10 to 30 cm (4 to 12 inches) in diameter (need to check values). The flowers are individually fairly small, ~16 mm (0.6 inches) in length, but there can be hundreds of flowers open at once on a single plant, making a showy display. The largest most-floriferous plant seen by Bruce Watts had at least 1,400 flowers open at once; the longest side of the triangular ruler in the linked picture is seven inches.
In Garner Valley, it grows mostly in shady north-west-facing slopes in the pebbly / rocky Bautista Formation, an alluvial formation weather from the ancestral Santa Rosa Mountains. Outside of the north-west-facing slopes, it can also grow on the north side of chamise plants, or in openings shaded by Jeffrey pines. However, young post-fire plants are happy to grow in full sun in rocky areas.
P. californicus appears to germinate only after a fire and then persists for at least decades. The PCT north of the Cedar Spring Trail was covered in places by large, very-happy plants growing in full sun in 2018, five years after the 2013 Mountain Fire. In contrast, the PCT south of the Cedar Spring Trail, which last burned ~25 years ago, has a much smaller number of plants that now are mostly confined to more shady areas. The last fire in Garner Valley was ~45 years ago, which may be why the plants are only found in shady areas there.
Few plants bloom in dry years such as 2018, but in wet years such as 2017 and 2019, essentially every plant is covered in bloom.
The geographic distribution of this species, from vouchers known to SEINet, is shown in Fig. 2.
Fig. 2. Left: The entire known population of Penstemon californicus from vouchers, as retrieved from SEINet on 30 July 2019. Right: The entire known population in California. Most of the voucher locations in this map were georeferenced from vague localities, making the Garner Valley distribution appear more extensive than it actually is; see The 2019 Bruce Watts Census for accurate maps.
There have been reports of P. californicus from other locations, but we consider these reports unreliable, for the following reasons:
- Aguanga, just north of Palomar Mountain, voucher by the Parish brothers from 18 June 1882. However, one of the four vouchers in this collection event also has a label on it from Brandegee from San Pedro Martir in Baja California. Since no one else has ever observed this species in Aguanga in the ensuing 137 years, we doubt this voucher is actually from Aguanga.
- "Cactus Valley" at SnBr and "north of Sage", from the CNDDB, as reported in the Western Riverside County Multiple Species Habitat Conservation Plan, and considered "doubtful" by them. No voucher exists for those reports.
- "Tenaja Road in the Santa Rosa Plateau", also reported in the Western Riverside County Multiple Species Habitat Conservation Plan. No voucher exists for that report.
- Vouchers from Siskiyou County in northern California and from Tennessee. These are surely misdeterminations.
Some of the misdetermined plants may actually be P. heterophyllus, a much more abundant and widespread species, which is somewhat similar. It has longer leaves (> 20 mm) and magenta to blue flowers, compared to the shorter leaves (< 15 mm) and purple to bluish-purple flowers of P. californicus.
Copyright © 2008-2019 by Bruce Watts and Tom Chester.
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Comments and feedback: Tom Chester
Updated 22 August 2019.