Flora of Clark Valley Area


Flora of Clark Valley Area

This checklist is a start at a flora of the Clark Valley Area. It consists of 157 taxa. Of those 157 taxa, we observed 121 in five different field surveys, and 110 of the 157 taxa have been vouchered here.

The checklist is current as of 11 February 2020, but the following text is from a previous version of this page done in the year 2008.

The floristic area denoted as the Clark Valley Area is delineated by the region outlined in red in the following map:

Only a single road traverses this area, the Rockhouse Canyon Road, on the western side of the Valley (see map below). There is also a private road that accesses private land on the north side of Clark Lake.

The western boundary of this area is the ridgeline / drainage divide of Coyote Mountain and its extension northward, to include the entire drainage basin of Butler Canyon / Rockhouse Canyon up to the San Diego County border with Riverside County.

The eastern boundary is mostly at the 3000 foot elevation contour of the Santa Rosa Mountains. The southeastern boundary is placed just a bit to the west of the Villager Peak Trail and Rattlesnake Canyon, since those two areas are more naturally included in the neighboring floristic area.

The southern boundary is set along Highway S22 to divide Clark Valley from the Badlands. Although this boundary is somewhat arbitrary, S22 gives a well-defined boundary.

For more information about Clark Valley, including pictures from our surveys, see Borrego Desert: Clark Valley.

Voucher Records

The voucher search was redone on 24 December 2016. This time only vouchers from Clark Valley itself and the immediately-surrounding areas were accepted. The following text has not been changed from the previous search.

The vouchers come from a search on 8 December 2008 of the Consortium of California Herbaria. The Consortium records were searched for San Diego County specimens that contained the word Clark in the locality (297 vouchers), as well as records with coordinates that fell within a rectangle that encompassed this area (369 vouchers). Duplicate vouchers, vouchers outside this area, and vouchers determined only to the genus that had more than one possible species, were removed.

This process yielded a total of 226 vouchers of 133 unique taxa.

The dominant collectors in the Consortium records were Larry Hendrickson and Kim Marsden and vice-versa, 83 vouchers; R. Mitchel Beauchamp, R. C. Pierce, 71 vouchers; and Bill Sullivan, 31 vouchers. These three sets of collectors accounted for 185 of the 226 vouchers, 82% of the total.

The locations of the vouchers are plotted in the following map, which also shows the boundaries of this region in more detail:

Because many vouchers share the same location, there are far fewer than 226 points plotted above.

Field Work

Field work has been added from 3/7/09, 12/19/09, and 12/27/16, but the following text has not yet been updated.

Three different areas within the Clark Valley area have been field surveyed. On 27 December 2007, James Dillane, Wayne Armstrong and I surveyed the 2.7 miles of the Alcoholic Pass Trail on Coyote Mountain that are on the Clark Valley side. We surveyed only for species not previously found on the southwestern side of the trail, so this survey was very incomplete. That portion of the trail is shown in green on the following map:

On 9 and 12 December 2008, Mike Crouse and I surveyed the two different routes shown in the following map :

We surveyed 5.75 unique miles on 9 December 2008, and 5.7 unique miles on 12 December 2008.

We also scanned the slopes of the nearby portion of the Santa Rosa Mountains for the elephant trees, Bursera microphylla, reported from that location (indicated by the labeled line in the above map), without finding them. However, since those trees were likely to be leafless at that time, they easily could have escaped our binocular survey from afar. This species was added to the checklist below based on sightings by Mark Jorgensen and Larry Hendrickson.

Note added 30 December 2016: We relocated the elephant trees on 19 December 2009 and vouchered one of them; see The Elephant Trees of Clark Valley.

A total of 63 taxa that could be fairly-confidently identified were found in those three December searches; 19 of those 63 taxa, 30%, are not among the vouchered species. A small number of additional taxa were found that could not be confidently identified at those times.

The unvouchered species do not come from any general problem with my identifications, since those unvouchered species include such easy-to-recognize taxa as Opuntia ramosissima, Psorothamnus spinosus, Ferocactus cylindraceus, and Encelia farinosa. This simply reflects the lack of botanical work for this area. It is possible that one or two of the unvouchered species might be misdetermined, since some of those determinations were made from dead plants.

Total Checklist

The total number of taxa presented below is 153, 148 of which are native. Of the 153 taxa, 63 were observed on one of the three field surveys, leaving 90 to be found from surveys at a more optimal time of year, or in locations not yet surveyed. Since 30% of the observed taxa are so far unvouchered, this may imply that the voucher list is on the order of 30% incomplete. However, since many of the unvouchered taxa are common, it may only imply that the most common taxa have not yet been vouchered.

Another source of incompleteness for this checklist is that most of the area has never been surveyed, especially the steep lower slopes of the Santa Rosa Mountains which may defy further surveys indefinitely. I estimate at most 24 square miles (62 km2) has had any survey within it, whereas 34 square miles (88 km2) has never had any survey within it. Using the standard relationship that the number of species scales as the 0.3 power of the area, this implies that (58/24)0.3 = 1.30 times more species should be found in the total area of ~58 square miles. This incompleteness is an additional factor to the incompleteness of the surveyed areas.

Thus the checklist below may be on the order of 1 / 1.32 ~ 60% complete, implying that the true number of taxa in this area might be roughly 260 instead of the 153 present below.

Checklist for the Clark Valley Area

This checklist is current as of 11 February 2020.

This checklist is only for a subset of the Clark Valley Floristic Area defined above, of just the floor of the Valley and the immediately-adjacent areas. Rockhouse Canyon / Butler Canyon has its own flora since that area is very different floristically from the desert floor area.


An asterisk before the common name indicates a non-native species.

The column with header #Pls gives the minimum number of observed plants from all the surveys in this area, up to a maximum of 99 plants. An x indicates we have observed that taxon but no abundance estimate was made. A V in this column indicates a species that was vouchered in this area that we haven't yet seen. An iN in this column indicates a species with an iNat observation as of 11 February 2020 that we haven't seen and that hasn't been vouchered. A FC in this column indicates a species on Fred Melgert and Carla Hoegen's plant list for this area for 11 February 2020 that wasn't seen, vouchered, or at iNat.

One species, Helianthus niveus ssp. tephrodes, has nr in this column since it may or may not be present in this area, but has been vouchered near this area. One voucher from 1933 has a vague location of North Borrego Valley on road to Clark Lake. Another voucher is from just east of this area on S22.

Version for printing, without lines and other text on this page: html (5 pages) or pdf Clickbook booklet (2 double-sided pages). (See printing instructions for an explanation of these options)

#FamScientific Name(*)Common Name#Pls
1PteCheilanthes parryiwoolly lipfern10
2AcaJusticia californicachuparosax
3AmaAmaranthus blitoides*mat amaranth20
4AmaAmaranthus fimbriatusfringed amaranthV
5AmaTidestromia suffruticosa var. oblongifoliaArizona honeysweet15
6ApoAsclepias subulatarush milkweed2
7ApoFunastrum hirtellumrambling milkweedV
8ApoPilostyles thurberiThurber's pilostyles1
9AstAmbrosia dumosaburroweed99
10AstAmbrosia salsola var. salsolacheesebush5
11AstBaileya pauciradiataColorado Desert marigold79
12AstBebbia juncea var. asperasweetbush4
13AstCalycoseris parryiyellow tackstemV
14AstCalycoseris wrightiiwhite tackstemV
15AstChaenactis carphoclinia var. carphocliniapebble pincushionV
16AstChaenactis fremontiiFremont pincushion20
17AstChaenactis stevioidesdesert pincushion99
18AstDicoria canescensdesert dicoria20
19AstEncelia farinosabrittlebush20
20AstEncelia farinosa var. farinosabrittlebushiN
21AstEncelia farinosa var. phenicodontapurple disk flower brittlebushiN
22AstEncelia frutescensbutton encelia2
23AstGeraea canescenshairy desert-sunflower99
24AstHelianthus niveus ssp. tephrodesAlgodones Dunes sunflowernr
25AstHelianthus petiolaris ssp. canescensgray desert sunflowerV
26AstIsocoma acradenia var. acradeniaentire-leaved alkali goldenbushV
27AstIsocoma acradenia var. eremophilatoothed-leaved alkali goldenbush99
28AstLactuca serriola*prickly lettuceFC
29AstLepidospartum squamatumscale-broomV
30AstLogfia arizonicaArizona herba impiaiN
31AstLogfia depressadwarf filagoFC
32AstMalacothrix glabratadesert dandelion30
33AstMonoptilon bellioidesdesert starx
34AstPalafoxia arida var. aridaSpanish needle40
35AstPectis papposa var. papposachinch-weediN
36AstPerityle emoryiEmory's rock-daisyV
37AstPeucephyllum schottiipygmy-cedarx
38AstPluchea sericeaarrow-weed99
39AstPsathyrotes ramosissimaturtlebackx
40AstRafinesquia neomexicanadesert chicory99
41AstSenecio mohavensisMojave ragwortiN
42AstStephanomeria exigua ssp. exiguaslender wreathplantV
43AstStephanomeria pauciflorawire-lettuce1
44AstTrichoptilium incisumyellow-headV
45AstTrixis californica var. californicaCalifornia trixis1
46AstVolutaria tubuliflora*Mediterranean desert knapweediN
47AstXylorhiza orcuttiiOrcutt's woody-asterV
48BigChilopsis linearis ssp. arcuatadesert-willowV
49BorAmsinckia intermediacommon fiddleneckiN
50BorAmsinckia tessellata var. tessellatabristly fiddleneckV
51BorCryptantha angustifolianarrow-leaved cryptantha99
52BorCryptantha barbigera var. barbigerabearded cryptantha1
53BorCryptantha barbigera var. fergusoniaeSanta Rosa Mountain bearded cryptanthaiN
54BorCryptantha costataribbed cryptanthaV
55BorCryptantha ganderiGander's cryptanthax
56BorCryptantha maritimaGuadalupe cryptantha5
57BorCryptantha micrantha var. micranthared-root cryptanthaV
58BorCryptantha nevadensis var. nevadensisNevada cryptanthax
59BorCryptantha pterocaryawing-nut cryptanthax
60BorEmmenanthe penduliflora var. penduliflorawhispering bellsiN
61BorEucrypta micranthadesert eucryptaiN
62BorHeliotropium curassavicum var. oculatumseaside heliotropex
63BorNama demissa var. demissapurple matiN
64BorPectocarya heterocarpachuckwalla pectocarya10
65BorPectocarya peninsularisBaja pectocaryaV
66BorPectocarya platycarpabroad-fruited combseed1
67BorPectocarya recurvatacurvenut combseedV
68BorPhacelia crenulata var. ambiguaheliotrope phacelia20
69BorPhacelia crenulata var. minutifloralittle-flowered heliotrope phacelia20
70BorPhacelia distanscommon phacelia10
71BorPhacelia ivesianaIves' phaceliaiN
72BorPhacelia neglectaalkali phaceliaiN
73BorPlagiobothrys jonesiiJones' popcorn floweriN
74BorTiquilia palmeriPalmer's coldenia1
75BorTiquilia plicataplicate coldeniaV
76BraBrassica tournefortii*Sahara mustard99
77BraCaulanthus lasiophyllusCalifornia mustardiN
78BraDescurainia pinnatawestern tansy-mustardFC
79BraDithyrea californicaspectacle-pod1
80BraDraba cuneifoliawedge-leaved drabaiN
81BraLepidium lasiocarpum ssp. lasiocarpumhairy-podded pepper-grass99
82BraSisymbrium irio*London rocket5
83BraStreptanthella longirostrislongbeak streptanthella5
84BraTropidocarpum gracileslender tropidocarpumiN
85BurBursera microphyllaelephant tree13
86CacCylindropuntia bigeloviiteddy-bear chollax
87CacCylindropuntia echinocarpasilver cholla22
88CacCylindropuntia ganderiGander's cholla15
89CacCylindropuntia ramosissimapencil cholla20
90CacEchinocereus engelmanniiEngelmann's hedgehog cactus1
91CacFerocactus cylindraceusCalifornia barrel cactus8
92CacMammillaria dioicaCalifornia fish-hook cactus1
93CacOpuntia basilaris var. basilarisbeavertail cactus1
94CamNemacladus glanduliferusglandular nemacladusiN
95CamNemacladus orientaliseastern glandular nemacladusiN
96CarAchyronychia cooperifrost matV
97CheAllenrolfea occidentalisiodine-bush99
98CheAtriplex canescens var. laciniataCaleb four-wing saltbush99
99CheAtriplex elegans var. fasciculatawheelscale10
100CheAtriplex hymenelytradesert holly3
101CheAtriplex lentiformis ssp. lentiformisbig saltbush65
102CheAtriplex polycarpacattle saltbush99
103CheMonolepis nuttallianaNuttall's poverty weed99
104CheSalsola paulsenii*Paulsen's Russian thistle99
105CheSuaeda nigrabush seepweed99
106CleCleomella obtusifoliaMojave cleomellaiN
107ClePeritoma arboreabladderpodV
108CleWislizenia refracta ssp. palmeriPalmer's jackass cloverV
109ConCuscuta californica var. papillosapapillate dodder3
110CraCrassula connatapygmy-weedFC
111CroCrossosoma bigeloviirock crossosomaV
112EupChamaesyce micromeraSonoran spurge1
113EupChamaesyce polycarpasmall-seeded spurge80
114EupChamaesyce setilobastarfish (Yuma) spurgeV
115EupCroton californicusCalifornia croton3
116EupDitaxis lanceolatanarrowleaf ditaxisx
117EupDitaxis neomexicanaNew Mexico ditaxisV
118EupStillingia spinulosaannual stillingia20
119FabAcmispon strigosusstrigose lotus1
120FabAstragalus crotalariaeSalton milk-vetch99
121FabAstragalus didymocarpus var. dispermusdwarf white milk-vetchV
122FabAstragalus lentiginosus var. borreganusBorrego milk-vetch99
123FabDalea mollissilky daleaV
124FabDalea mollissimadowny daleax
125FabLupinus arizonicusArizona lupine23
126FabLupinus shockleyidesert lupineiN
127FabParkinsonia floridablue palo verdeiN
128FabProsopis glandulosa var. torreyanahoney mesquite99
129FabPsorothamnus emoryiEmory's indigo-bush15
130FabPsorothamnus schottiiindigo bush50
131FabPsorothamnus spinosussmoke tree1
132FabSenegalia greggiicatclaw20
133FouFouquieria splendens ssp. splendensocotillo8
134GerErodium cicutarium*redstem filaree10
135GerErodium texanumTexas filareex
136KraKrameria bicolorwhite rhatany40
137LamHyptis emoryidesert-lavender10
138LamSalvia columbariaechia5
139LamSalvia vaseyiVasey's sage10
140LoaMentzelia affinisyellow blazing star20
141LoaMentzelia desertorumdesert blazing starV
142LoaMentzelia involucratabracted blazing star3
143LoaPetalonyx thurberi ssp. thurberiThurber's sandpaper-plant10
144MalEremalche exiliswhite mallow1
145MalEremalche rotundifoliadesert five-spotV
146MalHibiscus denudatusrock hibiscusx
147MalMalva parviflora*cheeseweediN
148MalSphaeralcea angustifoliacopper globemallow99
149MonCalyptridium monandrumsand cressiN
150MonCistanthe ambiguadead man's fingers99
151NycAbronia villosa var. villosahairy sand-verbena50
152NycAllionia incarnata var. incarnatasmall-flowered trailing four o'clockiN
153NycBoerhavia triquetra var. intermediafivewing spiderlingiN
154NycMirabilis laevis var. retrorsaBigelow's desert four-o'clockiN
155OnaCamissoniopsis pallida ssp. pallidapale suncupiN
156OnaChylismia claviformis ssp. peirsoniibrown-eyed primrose99
157OnaEremothera boothii ssp. condensataBooth's evening primrose7
158OnaEulobus californicusCalifornia suncup99
159OnaOenothera deltoides ssp. deltoidesdune primrose99
160OroOrobanche cooperiCooper's broomrapeiN
161PapEschscholzia minutiflora ssp. minutiflorasmall-flowered poppyx
162PapEschscholzia parishiiParish's poppyx
163PhrMimulus bigelovii var. bigeloviiBigelow's monkeyflowerx
164PlaMohavea confertifloraghost flowerV
165PlaPlantago ovatadesert plantain99
166PolAliciella latifolia ssp. latifoliabroad-leaf giliax
167PolEriastrum eremicum ssp. eremicumdesert woolly-star5
168PolEriastrum harwoodiiHarwood's woolly-stariN
169PolGilia stellatastar giliaiN
170PolLangloisia setosissima ssp. setosissimabristly langloisiaiN
171PolLinanthus jonesiiJones' linanthusiN
172PolLoeseliastrum matthewsiidesert calicoV
173PolLoeseliastrum schottiiSchott's calico99
174PolChorizanthe brevicornu var. brevicornubrittle spineflower3
175PolChorizanthe corrugatawrinkled spineflowerx
176PolChorizanthe rigidadevil's spinefloweriN
177PolEriogonum inflatumdesert trumpetx
178PolEriogonum thomasiiThomas' buckwheatx
179PolEriogonum trichopeslittle desert trumpet20
180PolPterostegia drymarioidesfairy bowties, threadstemiN
181ResOligomeris linifolialineleaf whitepuff99
182SimSimmondsia chinensisjojoba20
183SolLycium brevipes var. brevipesdesert boxthorn99
184SolNicotiana clevelandiiCleveland's tobaccoV
185TamTamarix aphylla*athel5
186TamTamarix ramosissima*saltcedar5
187VisPhoradendron californicumdesert mistletoe99
188ZygFagonia laevisCalifornia fagoniax
189ZygFagonia pachyacanthasticky fagoniax
190ZygKallstroemia californicaCalifornia caltropiN
191ZygLarrea tridentatacreosote bush99
192AgaHesperocallis undulatadesert lily50
193PoaAristida adscensionissix-weeks three-awnV
194PoaHilaria rigidabig galleta80
195PoaPhalaris minor*little-seed canarygrassiN
196PoaSchismus barbatus*Mediterranean schismus99
197PoaStipa hymenoidesIndian ricegrassiN

Voucher data provided by the participants of the Consortium of California Herbaria (ucjeps.berkeley.edu/consortium/)

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Copyright © 2008-2020 by Tom Chester, Mike Crouse, RT and Shaun Hawke, Keir Morse, and John Randall.
Permission is freely granted to reproduce any or all of this page as long as credit is given to me at this source:
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Last update: 11 February 2020