The Vascular Flora of Plum Canyon, Anza-Borrego Desert State Park
Larry Hendrickson, Tom Chester, James Dillane and Kate Harper
The "plums" of Plum Canyon are actually desert apricot, Prunus fremontii. Picture taken at the parking area at the end of the dirt road up Plum Canyon on 12 December 2012, of plants leafed out following monsoonal rain in August 2012. Most of the year the plants are leafless. Click on the picture to get a larger version.
Introduction
Google Earth View
Botanical Highlights
Procedure For Compiling The Checklist
Species Checklist
Introduction
Plum Canyon is a delightful canyon in the western part of Anza-Borrego Desert State Park. It is the first major canyon on the right (south) seen by people traveling from western San Diego County as they leave Sentenac Gorge and emerge into the desert proper. These eastbound travelers usually notice the showy red blossoms of chuparosa, Justicia californica, for the first time where Plum Canyon wash meets Highway 78 (SR78), where the first large population occurs.
As a result of its location in the Desert Transition Zone, Plum Canyon has an interesting collection of species, with good diversity. The plant checklist below contains 175 taxa, which range from lower desert species to even a few coastal species. The Canyon contains the westernmost extent at this latitude of some desert species, such as Carlowrightia arizonica, Arizona carlowrightia, and the easternmost extent of some coastal species, such as Selaginella bigelovii, Bigelow's spike-moss.
Even better, this Canyon has few non-native species. There are only four non-native species in its plant list (five if you count the possible non-native Mollugo cerviana), and they are not very abundant in the canyon. The biggest scourge of the desert, Brassica tournefortii, Asian mustard, is only found along SR78 at the bottom of Plum Canyon Wash. An aggressive weeding campaign led by the first author has kept this species mostly out of Plum Canyon.
The origin of the name Plum Canyon is not known for certain, but it is most likely to come from the abundant desert apricot, Prunus fremontii, in the canyon. Cultivated plums and apricots are very closely related, both in the genus Prunus, distinguished in Bailey as follows:
C. Fruit glabrous, usually with a slender pedicel that remains with it, the stone not prominently furrowed ... Plums
CC. Fruit pubescent, the pedicel short and separating at maturity, the stone usually furrowed on the margin... Apricots
Prunus fremontii has pubescent (= very short hairy) fruit, which clearly makes it an apricot, not a plum. But perhaps someone thought the dark color of the fruit at times was closer to a plum, and named the canyon for that.
This canyon is a favorite place for CNPS plant tours led by the first author; see photos from the March 2011 trip.
The entrance to Plum Canyon is 4.1 miles east of Scissors Crossing, and 2.7 miles west of the turnoff to Tamarisk Grove Campground and Yaqui Pass Road (S3).
Most passenger cars can easily drive the 1.6 miles up the sandy non-paved road from SR78 to a parking area where the canyon walls close in, preventing further car travel up the canyon (take the right-hand fork at mile 1.35). A fairly easy ~3 mile roundtrip, with 400 feet of elevation gain, walk up the canyon along the California Riding and Hiking Trail leads to a saddle overlooking Earthquake / Shelter Valley.
An even more interesting botanical trip is to start walking at SR78, to experience the full transition from the lower-elevation desert proper to the lower part of the desert transition zone near the top of the canyon. That walk is roughly 6 miles roundtrip with 900 feet of elevation gain, from 1700 feet to 2600 feet.
For botanists, one of the things that makes the walk along the entire canyon / wash special is that one is following the footsteps of California's first botanist, Willis Linn Jepson, the "Botany Man", who wrote the first manual on the flora of California.
Lower Plum Canyon was called Wagon Wash in those days, and was part of the wagon route from Earthquake / Shelter Valley to Yaqui Well. The old route heading west branched at the top of Plum Canyon; the California Riding and Hiking Trail follows one of the branches south from Upper Plum Canyon to North Pinyon Mountain Road in Earthquake / Shelter Valley. The other branch headed west down to the Sentenac Cienega area. (see map of Wagon Wash; Wray 2004 The Historic Backcountry: A geographic Guide to the Historic Places of the San Diego County Mountains and the Colorado Desert; and the 1913 topo map with the vegetation mapping showing the routes.
Today it seems like this route could never have been passable by wagons in some places. However, at least some of the rockslides creating impassable stretches appear fresh, and may have occurred after the wagon route was abandoned. In fact, the construction of the wagon route may have precipitated at least some of these rockslides by undercutting the slopes.
There is at least one area of upper Plum Canyon where the trace of the old wagon road is still visible, on the stretch just below the saddle (see also version with the old wagon road marked).
See Road Timeline in the Borrego Desert Area for dates of road construction that bypassed this Wagon Road.
Some links to photographs of Plum Canyon and its plant species:
- Keir Morse's 259 photographs from Plum Canyon on 5 March 2011.
- Keir Morse's 305 photographs from the canyon immediately east of Plum Canyon on 27 March 2011
- James Soe Nyun March 2011
- Kim Davis and Mike Stangeland 16 March 2010 including a beautiful photo of the canyon itself.
- Narca Moore-Craig March 11, 2011
- John and Evelyn Boucher 17 April 2010
- Doug Taron December 03, 2008
Google Earth View
Google Earth View of Plum Canyon and points east as seen using a vantage point at 6000 feet elevation from just south of Scissors Crossing looking northeast. Some features are labeled (see text below). The North direction is indicated in the upper right corner. Click on the picture to get a larger version. See also unlabeled version.
In the Google Earth View, the Plum Canyon drainage is outlined in red, with two saddles on the ridgeline dividing it from Earthquake / Shelter Valley shown in red diamonds. Blue lines show our survey routes on 12 and 21 December 2012. The northernmost route corresponds to the old Wagon Road built by John McCain sometime after 1895 and prior to 1913, which was only superceded in 1922 when SR78 was finished through Sentenac Gorge. Many traces of the old Wagon Road are still visible along most of its route on the Sentenac Cienega side of the Plum Canyon Saddle, but only a few traces are visible on the hike from the Plum Canyon Parking Area to the northernmost saddle.
The short Plum Canyon hike from the Parking Area goes to the northernmost of the two saddles shown on the map. However, there are no signs telling the hiker when to exit the main canyon in order to reach it. As a result, many hikers end up continuing up the main wash in a direction away from the saddle overlooking Earthquake / Shelter Valley! Or they take the California Riding and Hiking Trail to the southwest ridgeline of Plum Canyon. Or if the first turnoff is missed, but the second turnoff is taken, hikers end up at the southern of the two saddles shown on the map, which is just a bit longer.
Botanical Highlights
Willis Linn Jepson's Comments
As mentioned above, one of the botanical highlights is being in an area where Jepson himself collected 72 vouchers in 1920 and 1928. His fairly extensive notes in his field books, along with his vouchers, reveal what it was like 85 and 93 years ago. After our next survey in prime time, to make our observed list more complete, we'll do a detailed comparison of what we see now to conditions nearly a century earlier (see also below).
Jepson collected 72 vouchers from Wagon Wash in April 1920 and April 1928. His Field Books that describe the area, including the geography, plants and animals, and his collections, are all online:
- 1920 (vol. 37, pages 143-145, 147, 151, 157; collections #8766 to 8950), including a map of Wagon Wash, and
- 1928 (vol. 46, pages 193-214; collections #12,463 to 12,539).
In the Field Book pages, click on the upper right arrow to "turn the pages" in his field book. There are links to the online page for each of his vouchers that usually give a more-current name for each voucher. We've transcribed some of his pages; click on the link at the bottom of the pages when you see Read transcription. If you don't see that link, we encourage you to transcribe a page or two.
- 1928 (vol. 46, pages 193-214; collections #12,463 to 12,539).
Jepson's description of Plum Canyon = Wagon Wash from 1920 is still an accurate overview today:
This wash, from its junction with the San Felipe region to the summit of the pass is about 2 3/4 miles. The lowest half mile is Smoke Bush (Dalea spinosa = Psorothamnus spinosus), very much scattered. The next 1 1/2 miles is Hyptis emoryi which is very abundant and gives a distinct character to this part of the wash. The next half-mile is Desert Apricot (no. 8769; Prunus fremontii) which is abundant; the last 1/8 mile is no. 8772, Coleogyne ramosissima, dominant at very summit; but not extending down far. The 1/8 mile below it is most interesting for the Bernardia (no. 8775). [vol. 37, p. 157]
Jepson's notebook has Ayenia instead of Bernardia, but his voucher is determined as Bernardia, which is indeed an interesting species at that point in the Canyon today. We have not yet found any Ayenia at that point in Plum Canyon.
When Jepson said not extending down far for the Coleogyne ramosissima, he meant within Plum Canyon, on the east side of the summit, since that species extends all the way down to Sentenac Cienega on the west side of the summit.
And Jepson's admonition that desert botany requires careful scrutiny is just as valid today:
Many things show only a single individual, so far as we notice. For example, only one individual of Cassia armata Wats. was found. The desert, therefore, requires careful scrutiny - all the more in that certain things are everywhere so omnipresent. It is, too, easy to walk over inconspicuous plants in the desert sands, such as Nemacladus, no. 12,486. [vol. 37, p. 202]
Even in 1920 Erodium cicutarium, redstem filaree, was a problem. (In fact, the earliest botanists to explore California often found it.) Jepson commented:
I have not mentioned Erodium cicutarium this trip very much but everywhere in the desert one finds it. When the sandy granite is very dry it covers the country with small plants; even where desert plants (annuals) do not get along well. [vol. 37, pp. 152-153.]
Jepson clearly enjoyed Plum Canyon. In 1928 he wrote:
We move down the next day, Apr. 20, through Sentenac Canon, and turn up, off the road, into the lower part of the Wagon Wash, a hundred yards or more, and make camp. It is still very windy but we spend the day botanizing in the wash. In this locality I collect nos. 12,473 to 12,510. We spend the day and night here. It is a fine camp in a fine country for botanizing. [vol. 46, pages 195-196]
One big difference from 1928 is that we have not yet found Eriogonum plumatella in Plum Canyon. Jepson wrote:
There is a great deal of this in the wash called Wagon Wash. It forms colonies and makes a marked stand in places where there is little other vegetation. It also grows as scattered individuals on the first bench above the wash (3 to 5 ft. higher) scattered amongst the creosote bushes and cacti in open places. [Jepson originally called this E. palmeri, but crossed the name out on p. 201 and replaced it with E. plumatella; vol. 46, p. 207]
In our surveys of the length of Plum Canyon on 12, 21, and 28 December 2012, and 2 January 2012, we found not a single individual of E. plumatella! Nor has the first author found any in his extensive explorations of this Canyon. We did find a single plant in the wash immediately east of Plum Canyon Wash, but none others in a 7 mile exploration of that wash and canyon.
It is possible that in 1928 Jepson was referring to San Felipe Wash in the vicinity of Plum Canyon. San Felipe Wash was probably the wagon route after descending Plum Canyon.
Other Botanical Highlights
- This canyon is the type locality for Nemacladus glanduliferus, from Jepson's collection #8766 from 24 April 1920 (Picture of voucher).
- This canyon is also the type locality for a variety of Prunus fremontii that is no longer recognized as being distinct from the rest of the species, var. pilulata, from Jepson's collection #8769 from 24 April 1920).
Jepson gave its distinguishing characteristics as:
Leaves orbicular, more or less truncatish or subcordate at base, 5 to 8 lines [10 to 16 mm] long; fruit (immature) subglobose, a little flattened, a little broader than long, 4 lines [8 mm] long.
He gave the other variety as having larger leaves, 0.5 to 1.5 inches (13-38 mm) long; with oblong-ovoid or elliptic-ovoid fruit, 4-6 lines long. You can see why floras no longer accept var. pilulata, since there is a continuum between it and other plants of this species. We've noticed no difference in the size of the leaves of plants in Plum Canyon. It is likely that Jepson's sample just happened to be of a plant with smaller leaves than normal.
- This canyon has the easternmost population of Selaginella bigelovii in this latitude region of San Diego County, the Scissors Crossing area.
- This canyon is the only known location of Calyptridium parryi var. arizonicum in California (see a photograph of it from here). The first author collected this taxon here in two different years, on 16 April 2004 (#162) and 22 March 2008 (#2766) (see photograph of one voucher). As a result of these collections, it was one of the new taxa in the 2012 Second Edition Jepson Manual Treatment.
Note that the first collection of this taxon was only #162 of all his collections, showing you don't have to be a long-time collector in order to find something new for the flora of California!
The first author suspects that it might not be a coincidence that this Arizona taxon has appeared in Wagon Wash, given the amount of traffic from Arizona that must have occurred along this route in the past.
In fact, we know of two other species introduced in the vicinity of this area from points east:
- the Arizona long-horned devil's claw, Proboscidea parviflora ssp. parviflora, was introduced to the Banner Queen Ranch from a load of hay from Arizona in the mid-1980s.
- a waif of Crotalaria juncea, sunn hemp, was discovered growing in Sentenac Canyon by Kate Harper on our 12 December 2012 trip as she was driving through the gorge on the very day of our field work in Plum Canyon (we vouchered this plant, which had failed to produce any seeds). This single plant almost undoubtedly came from the numerous hay trucks that pass through Sentenac Canyon each day from the Imperial Valley and/or Colorado River hay fields.
Of course, it is also possible Calyptridium parryi var. arizonicum is native here, and simply not previously discovered here. For example, Jordan Zylstra was the first to recognize that the Sarcostemma cynanchoides at Pinyon Flat on the north side of the Santa Rosa Mountains was actually the only California population of the Arizona species Sarcostemma crispum. There is a known relationship between the plants along the east PR in California and plants at the eastern edge of the Sonoran Desert in Arizona (see below).
- This canyon has only the seventh known location of Carlowrightia arizonica in California, found by James Dillane, Tom Chester and Kate Harper on 12 December 2012. This species is only found in fairly small numbers at each of the seven locations.
Five of the seven populations, including this one, are in an area only 14 miles long and a few miles wide, all north of Plum Canyon except for the fairly nearby Mine Canyon population, with the other two populations disjunct by 9 miles and 20 miles to the south of this location. Only two of the seven populations made it into the 2012 Second Edition Jepson Manual Treatment, since most of the other five populations have only been recently discovered.
The last two highlights show that there is still much to be learned about the flora of California, with surprises waiting in many areas.
Both of these two species are disjuncts from Arizona, which shows that this area has some additional affinity to the flora of southwest Arizona other than the lower-elevation widespread species such as creosote and ocotillo. These disjunct species are separated from their Arizona siblings with a large area in-between currently without any of these species. The connection probably occurs during the cool phase of the Ice Ages, which lasts some 90% of one glacial cycle, when these species may expand their ranges so that the Arizona and California populations approach each other more closely. There have been roughly 24 such cycles, each lasting ~100,000 years, in the last 2.4 million years since the Ice Ages began.
Long-distance dispersal is also a possibility, but the number of other disjuncts, such as Arctostaphylos pringlei at higher elevations, makes a geographic connection of the range of these species during wetter, cooler times more likely.
Procedure For Compiling The Checklist
The Checklist was compiled from two sources:
- Fieldwork done on
- 12 December 2012 by Tom Chester, James Dillane and Kate Harper;
- 24 December 2010 by Kate Harper, adding two species (Senna covesii and Delphinium parishii ssp. subglobosum) from a mostly-hiking trip;
- 21 December 2012 by Tom Chester, James Dillane and Jim Roberts;
- 5 March 2011 by Keir Morse, adding four species from his photographs
- 27 March 2011 by Keir Morse in the canyon immediately east, adding six species as target species to the Plum Canyon list;
- 28 December 2012 by Tom Chester and Keir Morse, mostly in the canyon immediately east;
- 2 January 2013 by Tom Chester in the south branch of upper Plum Canyon; and
- 22 March 2013 by Tom Chester, Adrienne Ballwey and Kate Harper in the north branch of upper Plum Canyon, from the parking area to the saddle.
- Vouchers compiled from a search of the Consortium of California Herbaria on 11 December 2012 by Tom Chester.
The areas surveyed by the 12 and 21 December 2012 fieldwork are shown by the blue lines in the Google Earth View shown above.
The fieldwork on 21 December 2012 was primarily to find traces of the old Wagon Road, with only incidental botanizing.
The 12 December 2012 fieldwork was used to compile a species list, with a GPS location for at least one occurrence of every species, and to estimate abundances for each observed species. Note that the fieldwork list is extremely incomplete for annuals and perennials, since it was made from field trips at the worst-possible time of year, in late fall, which covered only a small area of the canyon along the main hiking route from SR78 to one of the several saddles at the top. We did not attempt to identify dead annuals except for those whose determinations were unambiguous from their remnants. The abundances for those dead annuals may be severely underestimated.
A species list was compiled from the 24 December 2010 fieldwork, but no GPS locations or abundances were recorded.
Species lists were not compiled from the other fieldwork. The 21 December 2012 and 2 January 2013 fieldwork noted any new species, and increased the abundances of a number of species. Notes and photographs from the other trips were used to add species to the plant list.
The 27 March 2011 and 28 December 2012 fieldwork was done primarily in the canyon directly east of Plum Canyon. Because the Plum Canyon List is incomplete for annuals and perennials, species seen only in that canyon were added to the Plum Canyon list as target species, ones to be looked for in Plum Canyon, and so identified in the checklist below.
The fieldwork found 111 distinct taxa in Plum Canyon, plus five additional taxa from the canyon to the east, for a total of 116 taxa.
Vouchers were obtained from three separate searches:
- using coordinates, for the rectangular box from 33.09 to 33.13° north latitude and -116.44 to -116.40° east longitude which included an area slightly larger than just Plum Canyon;
- vouchers with Plum Canyon in their localities; and
- vouchers with Wagon Wash in their localities.
Vouchers by Jepson were examined for "missing numbers", resulting in the addition of two vouchers.
Duplicate vouchers were removed, and the localities were reviewed manually to remove ones not in Plum Canyon. Six vouchers were badly georeferenced; 134 were clearly from outside Plum Canyon, with most in Sentenac Canyon or along SR78 outside the Plum Canyon area. 18 vouchers were from wash 300 yds W of Plum Canyon, which drains into the San Felipe River just upstream from Plum Canyon Wash, and hence were excluded.
Iti isn't clear whether the ten Jepson vouchers from 22 April 1928 were from the south fork of Plum Canyon, or from the entirely-separate canyon immediately east of Plum Canyon. Near SR78, the wash from the separate canyon is only 400 feet east of Plum Canyon Wash. He wrote:
In the morning Apr. 22 we drove back to Wagon Wash and I walked up the wash and into Mule-track Canon, the large canon to left of Wagon Wash Canon, and collected cacti.
Yet more confusingly, most of his vouchers from that day give Wagon Wash as the locality, with only two of the ten vouchers giving Mule-track Canyon in its locality, one of which also said Wagon Wash.
We have included his vouchers in this Checklist for now, but may exclude them in the future if some of the vouchered species are not found by us in the field in Plum Canyon. In the checklist below, two species were vouchered only from this set: Castilleja foliolosa and Pleurocoronis pluriseta.
One voucher determination was not accepted, of Opuntia wolfii = Cylindropuntia wolfii, by Jepson in 1928, JEPS66889. This species lives only much farther south, and hence this is unlikely to be the correct determination. It is most likely this is a specimen of C. ganderi, which was not recognized until 1938.
One voucher simply determined as Agave, also collected by Jepson in 1928, JEPS43125, was taken to be A. deserti, which is the only Agave species present in the Borrego Desert.
A few taxa were combined, when some were given as the species and others as the subspecies, and it was clear that only a single taxon was present.
That left 232 vouchers, of 122 distinct taxa.
The top collectors in Plum Canyon are:
| # Vouchers | Collector(s) |
|---|---|
| 78 | Larry Hendrickson |
| 72 | W. L. Jepson |
| 28 | Jeannie Gregory, John Gregory |
| 22 | Jon P. Rebman, J. Gibson, A. Winner, & misc. botany vols. |
| 10 | Bill Sullivan |
The union of the checklist from the fieldwork and the vouchers contains 175 taxa. Of those 175 taxa, 63 taxa were found in both the fieldwork and the vouchers; 59 were found only in the vouchers; 48 were found only from the fieldwork; and 5 taxa are listed as target species after being found in the canyon to the east.
Nearly all of the 59 species that were vouchered, but not seen in our fieldwork, were annuals or perennials that one would not expect to see in December. All of the 48 species seen in the fieldwork, and the 5 target species, that do not have vouchers in Plum Canyon have vouchers elsewhere in the Borrego Desert; most of those have vouchers from the immediate area surrounding Plum Canyon.
Species Checklist
The Checklist follows the 2012 Jepson Manual Second Edition with only a few exceptions.
The Checklist is sorted first by the eight evolutionary categories (clades) used in the 2012 Second Edition Jepson Manual - lycophytes, ferns, etc., to eudicots and monocots - and then by family and scientific name. The clades are labeled in the Checklist. Note that this changes the order of presentation of the taxa from that of the 1993 First Edition.
The family name is abbreviated to the first six characters in order to save space in the table rows.
An asterisk before the Common Name indicates a non-native taxon.
The column labeled #Pls gives a minimum estimate of the number of plants from the field surveys, up to a maximum of 99 plants, for species seen in the field surveys for which abundances were noted. The main intent of this estimate is to indicate the species for which we found very few plants. If the species was added from Keir Morse's photographs from 5 March 2011, the column contains his initials, KM. If the species was seen only in the canyon immediately to the east, it is present in the list as a target species, one to be looked for in Plum Canyon, and the column contains TGT.
The column labeled #V gives the number of vouchers in Plum Canyon.
The scientific name is linked to the latest online Jepson Manual description for each species, which also gives the months in which each species flowers. That link also gives a map of where the species occurs in California; a plot of elevation vs. latitude for California; and a histogram of the voucher collections by month.
A few species may not have working links, if their names have been updated more recently (such as Mimulus diffusus, which is still listed under M. palmeri in the online flora), or if they are reserved-judgment taxa which are listed in the entry for another taxon name. However, as of 26 December 2012, the Jepson Manual links have all been updated to link to the parent species for the taxa without their own entries. Taxa linked to anything other than the Jepson Manual link for the full scientific name used below have been indicated with a ^ after the scientific name, and are discussed here.
The common name for most species in the checklist is linked to Calphotos to give pictures of most taxa. Of course, there is no guarantee that the Calphotos pictures are correctly identified.
Note that the link will not always return pictures, since not every species has pictures at Calphotos, and a number of species still have their Calphotos pictures under the Jepson Manual First Edition Names. Some links have been made to the Calphotos pictures using the First Edition Jepson Manual name, if there are no pictures under the Second Edition name. Of course, that may result in a link with no pictures if those the names of those Calphotos pix are updated in the future to the Second Edition names.
Note also that the links below will return only the specified taxon at Calphotos, and not any subtaxa; i.e., a link to Cryptantha barbigera will not return photos of Cryptantha barbigera var. barbigera. There may be additional pictures at Calphotos under a different scientific name such as the First Edition Jepson Manual name.
Some links, such as for Bochera perennans, go to special pages with more information on those species.
As of 26 December 2012, the picture links have all been updated to link to a page that has pictures. Taxa linked to anything other than the Calphotos page of their full scientific name used below have been indicated with a ^ after the common name.
If you find any links from either the scientific or common names below that do not work, please let us know so we can update them.
Version for printing, without lines and other text on this page: html (6 pages) or pdf Clickbook booklet (2 double-sided pages). (See printing instructions for an explanation of these options)
Voucher data provided by the participants of the Consortium of California Herbaria (ucjeps.berkeley.edu/consortium/).
We thank Jim Roberts for his help with the survey on 21 December 2012, and Keir Morse for the additions from his photographs, and for his help with the part of the 28 December 2012 survey in Plum Canyon.