Plant Guide to Vernal Pool Trail, Santa Rosa Plateau

Introduction and Explanation of Plant Trail Guides

Highlights of This Trail
Fieldwork Dates and Summary of List Changes With Time
Botanical Trip Reports
The Plant Guide
Comments On Specific Species


The Vernal Pool Trail has not just one, but two very unusual botanical features. First, it dramatically shows what California was like ten million years ago, and thus tells part of the story about the evolution of the California flora. Second, it is the only trail in our database that contains a vernal pool, with its unique fauna and flora that can be seen nowhere else in Southern California so readily.

California 10 Million Years Ago And Today

Ten million years ago, California was flat. There were no large mountains, no Sierra Nevada. The mountains that had previously existed (the ancestors of our current Sierra Nevada, for example) had been eroded away as the action from the Pacific plate sliding under North America had moved on to the Rocky Mountain area, and then ceased.

Sometime around 7-15 million years ago, an oceanic-floor spreading center was overridden by the Pacific plate, and the San Andreas Fault first became active. The dying spreading center pushed up the area that is now the San Onofre and Santa Margarita Mountains, and about nine million years ago erupted lava onto the surface of the Earth in the Santa Rosa Plateau area, which flowed over that ~flat surface. Estimates are that the lava covered an area 20 miles across, roughly centered on the Mesa de Colorado.

Because lava is highly resistant to erosion, portions of that lava are still here today as the land eroded away around it. That flat surface now is broken into mesas, including the Mesa de Colorado, which retain the flat surface of ten million years ago. Every other mountainous area of Southern California consists of rugged terrain, with average slopes of around 60°. But the Santa Rosa Plateau consists of flat-topped mesas, and gentle rolling hills where the lava has only recently been eroded. About half of the Vernal Pool Trail is on that lava. See Santa Rosa Plateau Geology for more information.

What biological story does this geologic history tell?

When California was flat, it received summer rain. As a result, the flora of California ten million years ago was not much different from that in the rest of the United States.

About five million years ago, the Sierra Nevada was uplifted, and the climate changed. The high mountains eventually caused the Jet Stream in summer to retreat to our north, and we lost our summer rain. As a result, we lost all our species that require summer rain, except those along watercourses where water was available in the summer.

Those riparian species - willows, sycamores, sedges, etc. - are ones that many Easterners can recognize as being familiar, and are remnants of the California flora from ten million years ago. They are very different from the rest of the California flora today. Those riparian plants still act as if they get summer rain. They lose their leaves in the winter, just when the rest of today's California flora is beginning to grow. Then they grow actively during the summer, when the plants of today's California flora are shutting down to get through the dry season.

Where did the non-riparian plants of today's California flora come from? They came mostly from Mexico, where they evolved in areas without summer rain.

When you walk on the Vernal Pool Trail, think of all the things that have happened since the lava was laid down! When you see riparian plants later, perhaps along the Adobe Loop Trail here, think of the ancestors of these species here ten million years ago, being more widespread and then retreating to the wet places. Think of all the flora now found in Kansas and New Jersey and even China that once was here, but which could no longer survive when the climate changed. When you see our grassland, oak woodland or chaparral plants, think of them migrating thousands of miles from Mexico to colonize land that was now suitable for them.

Such a story told by the rocks you walk on along the flat Vernal Pool Trail!

Vernal Pool Flora

Vernal Pools used to be common in Southern California, and their species were not rare. But humans have destroyed 90-95% of all vernal pools in Southern California, because we like to build our homes in the flat areas where they are found.

A general rule of biology is that the number of species is proportional to area to roughly the 1/3 power. What this means is that if you destroy 90% of an area, you lose half the species. They don't go somewhere else to live; they could survive only in the area where they were found.

As a result, we have already lost half the vernal pool species in Southern California. They are gone. Many of those species we never even knew existed since the pools were destroyed before they were surveyed.

The remaining plants have become endangered. They've become endangered not because they are rare delicate species, or on their way out in evolution; they've become endangered because we humans have killed them relentlessly.

Perversely, because we humans treasure rare things more than common things, we now value these vernal pool plants very highly (which is a good thing!). This trail allows a fantastic look at these plants because it contains a boardwalk over the largest pool at the Santa Rosa Plateau.

There are still many vernal pools left in Southern California, but most of them are on military or private land, and are not easily accessible. Furthermore, this is the only example of a basalt-based vernal pool. All the other pools in Southern California are underlain by hardpan, and the vast majority of them are much smaller than our Main Pool.

Highlights of This Trail

The botanical highlights of this trail are:

Number of Unique Taxa On This Trail

The following histogram gives the number of trails in my database that contain each taxon on this trail. I had 90 trails in our database when this histogram was made; 16 of those trails, including this one, are at the Santa Rosa Plateau Ecological Reserve. A number of "1" means the taxon has only been found only on this list, among all the trails in my database; numbers of "16" or smaller may indicate taxa found only in this area.

Number of Trails
Containing A Taxon
Number Of Taxa
On This Trail
% of Taxa
On This Trail
Total Taxa186100%

All taxa found on the trail are included in the above table, although the identity of one taxon still remains to be fully verified.

The taxa found only on this trail, or on only a few trails, or only mostly on trails at the Santa Rosa Plateau, are:

#allCommon NameLatin Name
1yellow carpetBlennosperma nanum var. nanum
1hooked popcorn flowerPlagiobothrys undulatus
1prostrate navarretiaNavarretia prostrata
1annual hairgrassDeschampsia danthonioides
1spotted downingiaDowningia bella
1smooth goldfieldsLasthenia glaberrima
1alkali mallowMalvella leprosa
1Orcutt's quillwortIsoetes orcuttii
1small-flower western flaxHesperolinon micranthum
1white-leaf monardellaMonardella hypoleuca ssp. hypoleuca
2woolly marblesPsilocarphus brevissimus var. brevissimus
2thread-leaved brodiaeaBrodiaea filifolia
2San Diego button-celeryEryngium aristulatum var. parishii
2willow weedPolygonum lapathifolium
2water crowfootRanunculus aquatilis var. capillaceus
2*Carolina canarygrassPhalaris caroliniana
2western toad rushJuncus bufonius var. occidentalis
2white fairy lanternCalochortus albus
2*English rye-grassLolium perenne
2southern foothill penstemonPenstemon heterophyllus var. australis
3tawny popcorn flowerPlagiobothrys fulvus
3common lomatiumLomatium utriculatum
3brown microserisStebbinsoseris heterocarpa
3Bolander's water-starwortCallitriche heterophylla var. bolanderi
3purslane speedwellVeronica peregrina ssp. xalapensis
3clover fernMarsilea vestita ssp. vestita
3red-skinned onionAllium haematochiton
4*brome fescueVulpia bromoides
4warty spurgeEuphorbia spathulata
4*brass-buttonsCotula coronopifolia
5*Mediterranean barleyHordeum marinum ssp. gussoneanum
5spike primroseEpilobium densiflorum
5chocolate lilyFritillaria biflora var. biflora
5gray sageSalvia apiana X S. mellifera
6shining peppergrassLepidium nitidum var. nitidum
6western buttercupRanunculus occidentalis

Fieldwork Dates and Summary of List Changes With Time

The following table gives the dates the trail was walked and taxa recorded. After each visit, the table gives the total number of taxa on the list and the breakdown of the taxa without positive identification. See Explanation of Plant Trail Guides to understand the symbols below.

Visit DateVisit ## taxa# "?"# "sp"# "~"# "ssp"
12/15/20011709  1
2/4/20022878  1
2/21/200231208  1
3/4/2002413214  1
3/13/200251297  1
3/20/200261302  1
4/10/200281344  1
4/17/200291364  1
4/28/2002101393  1
5/5/2002111393  1
5/10/2002121390 11

I didn't keep track of the changes separately for 3/10/05 and 3/16/05. Prior to 3/10/05, the last portion of the trail was different, which affected only a single species. The 4/7/05 numbers reflect the new alignment of the trail, and also include a new taxon found on Ranch Road near the end of the trail that appeared for the first time in 2005. On 10/15/05, I added the section along Ranch Road, resulting in the addition of 8 taxa. Hence there are two entries in the table above for 10/15/05; the first one is for the previously-defined route.

In addition to the trips above, which concentrated on the plant guide, I made literally dozens of trips in 2001 and recorded the plants that were blooming. Those observations were used to augment the 2002-observed plant list on 2/21/02. Some of those species were never observed on this trail in 2002 due to the severe drought then.

I began using the "~" symbol in June 2002 and the "sp" symbol in August 2002; those categories were given the "?" symbol prior to those dates (we updated the 5/10/02 numbers to reflect our current usage.) I didn't record the numbers after some of the updates, especially the minor later ones.

Two new offtrail species were added from 9/12/05 fieldwork, and another new offtrail species was added from 9/23/05 fieldwork, but the rest of the trail wasn't botanized.

Botanical Trip Reports

List of Plants in Bloom 24 March 2003

30 March 2004

See also many previous botanical trip reports present in Observations of Flowering Plants and the Vernal Pools: Detailed Observations From Each Hike, organized by year, linked from the main page.

The Plant Guide

Version for printing, without lines and other text on this page: html (8 pages), pdf Clickbook booklet (2 double-sided pages), or Large Type pdf Clickbook booklet (4 double-sided pages). (See printing instructions for an explanation of these options)

The mileages have been fit to a detailed GPS recording of the trail up to mile 1.05. Those mileages should be accurate to 0.01-0.02 miles.

MileS#id?Common NameLatin Name#here#all
0.00   Trailhead on Via Volcano
0.00b  (puncture-vine, Tribulus terrestris)
0.00r sp(tumble pigweed, Amaranthus albus; annual goosefoot, Chenopodium sp.; telegraph weed, Heterotheca grandiflora; horseweed, Conyza canadensis; Rhodes grass, Chloris gayana)
0.00r1 *foxtail barleyHordeum murinum ssp. glaucum+40 / 213
0.00r2 *ripgut bromeBromus diandrus99 / 951
0.00r3 *shortpod mustardHirschfeldia incana99 / 951
0.00c4 *knotweedPolygonum arenastrum20 / 518
0.00r5 *Crete weedHedypnois cretica5 / 219
0.00r6 *short-fruited filareeErodium brachycarpum99 / 914
0.00r7 *wild oatsAvena fatua99 / 926
0.00l8 *sow thistleSonchus oleraceus20 / 541
0.00r9 blue dicksDichelostemma capitatum ssp. capitatum99 / 946
0.00r10 checkerbloomSidalcea malviflora ssp. sparsifolia99 / 925
0.00l11 *soft chessBromus hordeaceus99 / 940
0.00 12 *tocaloteCentaurea melitensis99 / 545
0.00r13 graceful tarplantHolocarpha virgata ssp. elongata99 / 914
0.00r14 rusty-haired popcorn flowerPlagiobothrys nothofulvus99 / 912
0.00 15 splendid mariposa lilyCalochortus splendens99 / 919
0.00r16 California plantainPlantago erecta1 / 113
0.00r17 soap plantChlorogalum pomeridianum var. pomeridianum20 / 518
0.00b18 *red bromeBromus madritensis ssp. rubens99 / 952
0.00r19 *pineapple weedChamomilla suaveolens10 / 319
0.00r20 *smooth cat's earHypochaeris glabra99 / 935
0.00 21 dove weedEremocarpus setigerus30 / 524
0.00r22 shining peppergrassLepidium nitidum var. nitidum99 / 36
0.00l23 dwarf lupineLupinus bicolor99 / 929
0.00l24 *Italian rye-grassLolium multiflorum99 / 917
0.00r25 purple clarkiaClarkia purpurea ssp. quadrivulnera99 / 925
0.00l26 *California burcloverMedicago polymorpha50 / 440
0.00b27 balloon cloverTrifolium depauperatum var. truncatum99 / 97
0.01l  Sign: "Reserve Fees $2 adults, $1 children"
0.01r28 Spanish cloverLotus purshianus var. purshianus30 / 431
0.01r29 earth brodiaeaBrodiaea terrestris ssp. kernensis99 / 97
0.01l30 muillaMuilla maritima99 / 97
0.01r31 purple sanicleSanicula bipinnatifida99 / 911
0.01r32 tawny popcorn flowerPlagiobothrys fulvus+99 / 93
0.01r33 ground pinkLinanthus dianthiflorus99 / 99
0.01l34 goldfieldsLasthenia californica99 / 912
0.01r35 common lomatiumLomatium utriculatum50 / 53
0.01r36 red maidsCalandrinia ciliata20 / 318
0.01l  Display Board
0.01 37 *nit grassGastridium ventricosum99 / 924
0.01b38 *hairy rattail fescueVulpia myuros var. hirsuta99 / 918
0.01r39 *slender wild oatsAvena barbata50 / 339
0.01r40 purple needlegrassNassella pulchra99 / 919
0.01r41 *prickly lettuceLactuca serriola99 / 942
0.01l42 yellow carpetBlennosperma nanum var. nanum99 / 91
0.01l  Sign: "Vernal Pool Trail (ahead); To Large Pool 0.7 mi; To Adobes 1.7 mi"
0.01l43 pygmy-weedCrassula connata50 / 228
0.01l44 silver puffsUropappus lindleyi99 / 926
0.01r45 *mouse-ear chickweedCerastium glomeratum5 / 219
0.01r46 owl's-cloverCastilleja densiflora+99 / 57
0.01r47 *windmill pinkSilene gallica20 / 233
0.01r48 *narrowleaf filagoFilago gallica20 / 245
0.01r49 brown microserisStebbinsoseris heterocarpa50 / 33
0.01l  (San Diego wreathplant, Stephanomeria diegensis)
0.02b50 California-asterLessingia filaginifolia var. filaginifolia30 / 951
0.03r51 *redstem filareeErodium cicutarium20 / 255
0.04l  (coast live oak, Quercus agrifolia var. agrifolia)
0.04r52 vinegar weedTrichostema lanceolatum20 / 514
0.05l53 one-sided bluegrassPoa secunda ssp. secunda10 / 323
0.05 54 *goldentopLamarckia aurea99 / 321
0.05r55 sharp-toothed sanicleSanicula arguta20 / 616
0.06l56 San Diego birdsfoot lotusLotus hamatus5 / 124
0.06l57 bajada lupineLupinus concinnus30 / 311
0.06l58 long-stemmed buckwheatEriogonum elongatum var. elongatum20 / 327
0.06l59 angel's giliaGilia angelensis40 / 114
0.06l  (In prickly-pear: Vasey's prickly-pear, Opuntia vaseyi; *bull thistle, Cirsium vulgare; California fuchsia, Epilobium canum ssp. canum; wild cucumber, Marah macrocarpus var. macrocarpus; and poison oak, Toxicodendron diversilobum.
  60 *sand spurreySpergularia bocconei+10 / 213
0.09r61 fringe-podThysanocarpus curvipes10 / 29
 l62 rattlesnake weedDaucus pusillus10 / 228
 r63 *scarlet pimpernelAnagallis arvensis10 / 232
0.10l64 San Diego morning-gloryCalystegia macrostegia ssp. tenuifolia+10 / 318
 l65 *hedge mustardSisymbrium officinale30 / 220
 r66 *white sweetcloverMelilotus albus10 / 17
0.11l  (large Engelmann oak, Quercus engelmannii)
0.11r67 *brome fescueVulpia bromoides / 4
0.11r68 blue larkspurDelphinium parryi ssp. parryi20 / 313
0.12r69 blue-eyed grassSisyrinchium bellum99 / 919
0.12b70 johnny jump-upViola pedunculata99 / 916
0.12l  Jct. Los Santos Trail. Enter mustard and wild oats "desert", crowding out natives, mostly on right.
0.12l  (California buckwheat, Eriogonum fasciculatum var. foliolosum)
0.13l  (telegraph weed, Heterotheca grandiflora)
0.14l71 *curly dockRumex crispus99 / 523
0.14r  (California everlasting in prickly pear)
0.15l72 Vasey's prickly-pearOpuntia vaseyi+10 / 224
0.15l  (coast live oak, Quercus agrifolia var. agrifolia)
0.16r73 San Diego wreathplantStephanomeria diegensis20 / 421
 r74 pin-point cloverTrifolium gracilentum var. gracilentum10 / 28
 r75 small-head field cloverTrifolium microcephalum10 / 110
  76 shooting starDodecatheon clevelandii ssp. clevelandii99 / 311
 l  Check specimens here for bloom to see if they are common spikerush, , or wire rush, Juncus balticus
0.20l77 *prickly sow thistleSonchus asper ssp. asper / 130
0.20l  Badger holes appeared here July 2002; nearly filled in by gophers in December 2002
0.20r78 *Mediterranean barleyHordeum marinum ssp. gussoneanum50 / 25
0.20r79 warty spurgeEuphorbia spathulata99 / 94
0.21r  Jct. short path to old percolation pit, now a mini-vernal pool, and ok to visit. Next 7 taxa at perc pit
0.21 80 hooked popcorn flowerPlagiobothrys undulatus99 / 21
0.21 81 Bolander's water-starwortCallitriche heterophylla var. bolanderi99 / 23
0.21 82 woolly marblesPsilocarphus brevissimus var. brevissimus50 / 22
0.21 83 spike primroseEpilobium densiflorum10 / 15
0.21 84 prostrate navarretiaNavarretia prostrata5 / 11
0.21 85 common spikerushEleocharis macrostachya99 / 311
0.21 86 thread-leaved brodiaeaBrodiaea filifolia50 / 42
0.22   Back on main trail
0.25l  (large Engelmann oak, Quercus engelmannii)
0.26l  Outer part of curve of trail is one of the best shooting star fields, accompanied by blennosperma and goldfields.
0.29l87 Two young Engelmann oaksQuercus engelmannii10 / 523
 r  (Check for Plagiobothrys arizonicus or intergrade with it)
0.34r88 western buttercupRanunculus occidentalis+50 / 96
0.34   Curve left
0.35b89 California poppyEschscholzia californica30 / 329
  90 *long-beaked filareeErodium botrys50 / 511
 r  Pristine field of purple needlegrass, Nassella pulchra
0.40l  Famous "see-through" tree shell in distance on left, with just bark left standing.
0.40r91 *(gazania)Gazania X (mounding hybrid)+1 / 16
0.42l92 nodding needlegrassNassella cernua99 / 516
0.42l  Jct. Trans Preserve Trail
0.43l  (coyote bush, Baccharis pilularis)
0.44r93 white everlastingGnaphalium canescens ssp. microcephalum7 / 336
0.45l94 Mexican rushJuncus mexicanus20 / 116
0.46r95 *winter vetchVicia villosa ssp. varia+99 / 119
0.47l  Display Board with story of Vernal Pool on one side, basalt weathering on the other.
0.48l  (laurel sumac, Malosma laurina))
0.49l  First large Engelmann oak, Quercus engelmannii, on the trail
0.49l96 laurel sumacMalosma laurina10 / 342
0.50l97 California everlastingGnaphalium californicum+30 / 442
0.55   Trail bends left
  98 *tumble pigweedAmaranthus albus3 / 212
0.61r99 *(bull thistle)Cirsium vulgare+1 / 117
0.63l  Begin main population of thread-leaved brodiaea, Brodiaea filifolia
0.64   Bench; Jct. loop trail around pool. Go right to pool, taking the loop counter-clockwise.
0.65b100 slender tarweedHemizonia fasciculata20 / 217
0.66   Begin boardwalk. The hooked popcorn flower makes the white color at the Pool.
0.66r101 purslane speedwellVeronica peregrina ssp. xalapensis10 / 23
0.66r102 common bedstrawGalium aparine+20 / 238
0.66l103 *rabbits-foot grassPolypogon monspeliensis20 / 222
0.66r104 annual hairgrassDeschampsia danthonioides20 / 11
0.66l105 San Diego button-celeryEryngium aristulatum var. parishii50 / 12
0.66r106 *brass-buttonsCotula coronopifolia10 / 24
0.66b107 spotted downingiaDowningia bella99 / 11
0.67r108 smooth goldfieldsLasthenia glaberrima5 / 11
0.67r109 willow weedPolygonum lapathifolium+1 / 12
0.67b110 alkali mallowMalvella leprosa40 / 21
0.68l111 knot grassPaspalum distichum99 / 27
0.68r112 Orcutt's quillwortIsoetes orcuttii1 / 11
0.68   Center of boardwalk
0.68r113 water crowfootRanunculus aquatilis var. capillaceus5 / 12
0.68c114 *grass polyLythrum hyssopifolia10 / 114
0.68r115 clover fernMarsilea vestita ssp. vestita10 / 13
0.69r116 *Carolina canarygrassPhalaris caroliniana1 / 12
0.71b117 *cut-leaved geraniumGeranium dissectum20 / 113
0.71   End boardwalk; continue on loop trail
0.71l  Blennosperma and goldfields patch
0.73r118 western toad rushJuncus bufonius var. occidentalis10 / 12
0.74   (Check for different Plagiobothrys, collinus?)
0.79   Spot from which pool pictures were taken for 2002 onward.
0.83   End loop trail; continue on Vernal Pool Trail to the right.
0.85   Spot from which pool pictures were taken for 2001.
0.85r  (In the prickly pear: coast-range melic, Melica imperfecta; bee plant, Scrophularia californica ssp. floribunda; and bicolored everlasting, Gnaphalium bicolor.)
0.88r  Badger holes appeared here April 2002, the first badger holes on the trail in my experience (since 1996). Nearly filled in by gophers in December 2002
0.89r119 *spring vetchVicia sativa ssp. sativa30 / 36
0.91l  Second set of April 2002 badger holes
0.91   End wheelchair-accessible portion of trail
0.91l120 coast live oakQuercus agrifolia var. agrifolia1 / 142
0.91l  Engelmann oak growing inside the coast live oak
0.92l121 coast-range melicMelica imperfecta10 / 243
0.92l  (Flat-topped bent Englemann oak off trail. It probably grew under another tree that is no longer present.)
 l  (hollyleaf redberry, Rhamnus ilicifolia, in prickly pear)
0.93l  View of Elsinore peak with ~6 antenna on it at ~10 o'clock
 l  (white sage, Salvia apiana)
0.94l122 bush lupineLupinus excubitus var. hallii5 / 110
0.94l123 lanceleaf dudleyaDudleya lanceolata1 / 120
0.95l124 bird's-foot fernPellaea mucronata var. mucronata1 / 130
1.00b  Field of shooting stars
1.01r  White variant of owl's-clover, Castilleja densiflora
1.04r125 tomcat cloverTrifolium willdenovii20 / 117
1.04r  California everlastingGnaphalium californicum+ /  
1.05   Trail turns right and drops off top of Mesa de Colorado
1.05l126 *white-stemmed filareeErodium moschatum20 / 120
1.05l127 coffee fernPellaea andromedifolia1 / 122
1.05l128 caterpillar phaceliaPhacelia cicutaria var. hispida50 / 116
1.05b129 wild-cucumberMarah macrocarpus var. macrocarpus5 / 144
1.05l130 leafy daisyErigeron foliosus var. foliosus1 / 143
1.06l131 poison oakToxicodendron diversilobum5 / 143
1.06r132 California fuchsiaEpilobium canum ssp. canum1 / 120
1.06r  common bedstrawGalium aparine+ /  
1.06l  (Nice stand of somewhat hidden blue dicks, Dichelostemma capitatum ssp. capitatum, San Diego pea, Lathyrus vestitus var. alefeldii, and south coast morning-glory, Calystegia macrostegia ssp. intermedia.)
1.06r  (white everlasting, Gnaphalium canescens ssp. microcephalum)
1.07l133 bicolored everlastingGnaphalium bicolor5 / 229
1.07r134 slender vetchVicia hassei10 / 36
1.07r135 pellitoryParietaria hespera var. hespera1 / 16
1.07l136 white-flowering currantRibes indecorum10 / 322
1.07r137 southern miner's lettuceClaytonia perfoliata ssp. mexicana20 / 225
1.07r138 *hedge parsleyTorilis nodosa20 / 114
1.07r139 San Diego peaLathyrus vestitus var. alefeldii2 / 221
1.07r140 south coast morning-gloryCalystegia macrostegia ssp. intermedia+10 / 119
1.07r141 blue wildryeElymus glaucus ssp. glaucus20 / 121
1.08 142 *(milk thistle)Silybum marianum+1 / 19
1.09r143 climbing bedstrawGalium nuttallii ssp. nuttallii10 / 330
1.09r  Bench
1.11r  Field of purple sanicle
1.12l144 toyonHeteromeles arbutifolia10 / 244
1.14l  (chocolate lily, Fritillaria biflora var. biflora)
1.15r  (Engelmann oak, Quercus engelmannii, with a few crown galls, lost two major limbs from main trunk in summer 2005)
1.17   Enter Fairy Lane, a short section of chaparral / coastal sage scrub lined with Fairy Lanterns (in season).
1.17b145 white fairy lanternCalochortus albus50 / 22
1.17b146 Torrey's scrub oakQuercus acutidens20 / 226
1.17r147 sticky cinquefoilPotentilla glandulosa ssp. glandulosa20 / 217
1.18b148 Pacific sanicleSanicula crassicaulis5 / 220
1.18r149 narrowleaf bedstrawGalium angustifolium ssp. angustifolium10 / 248
1.18r150 saw-toothed goldenbushHazardia squarrosa var. grindelioides20 / 235
1.18b151 deerweedLotus scoparius var. scoparius20 / 229
1.18r152 bush monkeyflowerMimulus aurantiacus10 / 142
1.18l  (sacapellote, Acourtia microcephala)
1.20r153 black sageSalvia mellifera30 / 240
1.20r154 sugar bushRhus ovata+5 / 225
1.20l155 *purple false-bromeBrachypodium distachyon20 / 16
1.20b156 chamiseAdenostoma fasciculatum20 / 137
1.20r157 southern honeysuckleLonicera subspicata var. denudata5 / 240
1.20r158 heartleaf penstemonKeckiella cordifolia2 / 227
1.22r159 small-flower western flaxHesperolinon micranthum50 / 31
1.23l160 chocolate lilyFritillaria biflora var. biflora50 / 95
1.23 161 yellow mariposa lilyCalochortus weedii var. weedii10 / 110
1.23l162 golden yarrowEriophyllum confertiflorum var. confertiflorum20 / 255
1.24b163 red-skinned onionAllium haematochiton10 / 33
1.24 164 *English rye-grassLolium perenne1 / 12
1.24   Local low point on trail
1.24r  (chocolate lily, Fritillaria biflora var. biflora in field of red-skinned onion, Allium haematochiton)
1.24l165 southern foothill penstemonPenstemon heterophyllus var. australis1 / 12
1.24r166 foothill needlegrassNassella lepida20 / 120
1.27l167 Eastwood manzanitaArctostaphylos glandulosa ssp. zacaensis5 / 211
1.28r168 white-leaf monardellaMonardella hypoleuca ssp. hypoleuca5 / 11
1.30r169 hollyleaf redberryRhamnus ilicifolia5 / 143
1.30   Cross drainage
 l  (One or two *olive trees, Olea europaea present in 2001 were removed in 2002.)
1.31   Local high point on trail
1.32   Interesting mushrooms, light brown with dark brown edge.
1.33r170 white sageSalvia apiana1 / 138
1.33r171 gray sageSalvia apiana X S. mellifera+1 / 15
1.34   Local low point on trail
1.35r172 narrow-leaved miner's lettuceClaytonia parviflora ssp. parviflora2 / 119
1.35r  (California peony, Paeonia californica)
1.35   Local high point on trail
1.36l173 blue elderberrySambucus mexicana1 / 148
1.36   End chaparral
1.37b  First large patch of chocolate lily, Fritillaria biflora var. biflora
1.37   Trail was rerouted in 2004 to eliminate the mudpit section. The new trail has many more chocolate lilies on it!
1.44l174 slender madiaMadia gracilis3 / 119
1.45r175 *oliveOlea europaea1 / 110
1.48   Cross small drainage
1.52r176 strigose lotusLotus strigosus10 / 133
1.53   Trail zigzags left
1.54r  White variant of dwarf lupine, Lupinus bicolor
1.54b177 Indian milkweedAsclepias eriocarpa1 / 117
1.57   Jct. Ranch Road. Turn right, toward adobes
1.59l178 *rose cloverTrifolium hirtum2 / 112
1.59r179 western ragweedAmbrosia psilostachya10 / 139
1.61b180 horseweedConyza canadensis5 / 140
1.61r  Jct. old Vernal Pool Trail; plants at Adobes not described here; most have been planted.
1.62l181 *little horseweedConyza bonariensis5 / 118
1.64l  (horehound, Marrubium vulgare)
1.66l182 fragrant everlastingGnaphalium canescens ssp. beneolens1 / 124
1.66l183~*Chinese elmUlmus parvifolia2 / 12
1.67r184 *Bermuda grassCynodon dactylon10 / 233
1.67r185 *English plantainPlantago lanceolata5 / 120
1.67   Jct. Adobes; guide doesn't include plants at Adobes, and resumes back at the jct. with the Vernal Pool Trail. There is a porta-potty at Adobes.
1.77   Jct. Vernal Pool Trail; guide continues west along Ranch Road toward Trans-Preserve Trail
1.92b186 stinking gourdCucurbita foetidissima5 / 19
2.06   Road curves right 90°
2.12   Jct. Hidden Valley Road; turn left
2.19   Jct. S. Trans Preserve Trail; end guide

Comments On Specific Species

Hordeum murinum ssp. glaucum. As I have also seen on the Mt. Wilson Toll Road in the San Gabriel Mountains; the Backbone Trail in the Santa Monica Mountains; and plants at my house in Fallbrook in San Diego County, these plants key perfectly to ssp. leporinum in Munz, but are perfect ssp. glaucum in JM. My id is due to my general conformance with the JM.

I suspect that the two subspecies are no longer separate in Southern California, due to hybridization of the formerly separate subspecies. I am accumulating data from many locations in Southern California to analyze this.

Plagiobothrys fulvus. This taxon, found here and in the adjacent San Mateo Wilderness Area, is disjunct from the rest of its species found in Northern California (NcoR, SNF, SnFrB), Oregon and Chile. The North American plants have been called var. campestris.

Castilleja densiflora. The two subspecies are supposedly geographically distinct, with ssp. densiflora found either in Los Angeles County north (Munz) or only in northern California (NcoR, c SNF, ScoR; JM), and ssp. gracilis found mostly in Southern California (ScoR, SW, n Baja CA).

However, the specimens here, and especially those at Daley Ranch, have more ssp. densiflora traits than those of ssp. gracilis! In particular, two out of three specimens in the population near the Main Pool clearly key out as ssp. densiflora, with a calyx of 12-13 mm, a lower corolla lip that widens gradually and pouches that are distinctly longer than deep. However, the ssp. densiflora specimens do not have bracts as long as the corolla and the corolla is exserted.

I have therefore decided to go along with the treatment by both the Western Riverside County Checklist by Roberts et al, and the Flora of the Santa Rosa Plateau by Lathrop and Thorne, where they have discarded the subspecies.

Spergularia bocconei. This weedy non-native species is on the Red List as a critically endangered plant in its native land, the United Kingdom! This is an excellent example of why non-native plants have unfair advantages in competition with native plants, and why "survival of the fittest" is not applicable here.

Calystegia macrostegia ssp. arida. About half the plants at the SRP appear to be ssp. arida, with the other half split between sspp. "intermedia" and "tenuifolia". It has long troubled me to be finding three subspecies in the small area of the SRP. Worse, the classification of a given plant has changed with time, which was extremely puzzling.

These difficulties were resolved when I found clear evidence that subspecies "intermedia" and "tenuifolia" are bogus. Hence I assign all the SRP plants to ssp. arida.

Opuntia vaseyi. The identification for these young plants came from plants with flowers near the Main Vernal Pool. Note that the JM calls this Opuntia Xvaseyi, but to my knowledge there is no strong evidence that this is a hybrid. These plants are certainly not hybrids produced from two separate parents; of course, hybridization may have been involved in the origin of this species. This species is found extensively in the SCo region, typically from a few to 20 miles inland from the coast, where it is the dominant species. Every single prickly pear that I have seen in the Santa Rosa Plateau Ecological Reserve is this species.

Gazania X (mounding hybrid); Cirsium vulgare; Silybum marianum. These weeds are eliminated whenever observed. Thus you will not necessarily see them on the trail. They are listed here because they were observed in those locations at one time, and hence are likely to occur again.

Ranunculus occidentalis. Lathrop and Thorne (1985) identified the species here as Ranunculus californicus, but they are in fact R. occidentalis. In particular, they generally have 5 petals, sometimes 6 petals, infrequently up to 12 petals, and the petals are ~round. These are both key characteristics of R. occidentalis, compared to the 9-17 petals and petal length ~ two times its width of R. californicus. They also have only the glabrous receptacles of R. occidentalis.

I examined the voucher specimens of Lathrop and Thorne at RSA, to see how they arrived at their species determination. One voucher was of a plant with 8 petals per flower! I've seen perhaps 1 in 1,000 plants like that at the SRP, and it is understandable that they keyed that one to R. californicus. A second voucher showed a plant with 5 petals per flower, our typical plant at the SRP. Thorne called that "R. californicus, appearing as R. occidentalis". (;-) Their third and last voucher showed a plant with 5 petals, with simply R. californicus as the id.

Thus the Lathrop and Thorne classification was based on an improbably-bad sampling of the plants at the srp, and is clearly wrong.

I have since found another population that appears to be similar to the SRP population at Palomar State Park. These two populations appear to be the southernmost outposts of R. occidentalis.

I have also found four occurrences of the true R. californicus population in Southern California, at Laurel Canyon in Orange County; East Grade Project Road in the eastern Palomar Mountains; and the Kelly Ditch Trail and Garnet Peak Trail / Penny Pines Trailhead in the Laguna Mountains. Those populations are quite different from these plants, with the expected 8 and more petals that are ~two times longer than wide.

The "problem" with a Ranunculus occidentalis id may be simply that this species is not supposed to occur south of the Tehachapi Mountains. This was the botanical wisdom prior to the discovering of these populations of plants at the SRP and at Palomar Mountain, since those areas had not been surveyed at the time that wisdom was stated. This is not a compelling reason to accept the other id, especially since the SRP contains other taxa that are not "supposed to be" in Southern California, such as Plagiobothrys fulvus.

Vicia villosa ssp. varia. Although a few plants grow immediately next to the trail (for the first time in 2003), the vast majority of the plants here are off-trail to the south, at the north base of the oak tree south of the Display Board. A large number of these annuals combine to provide a burst of purple color there, easily visible from the trail.

Gnaphalium californicum. There is a single small plant at the first location along the trail, which is easily missed. The largest collection of them is at mile 0.94.

Galium aparine. A single specimen was observed at the beginning of the boardwalk in 2002 and 2003; all other specimens are found at mile 0.95.

Polygonum lapathifolium. A single plant germinated in the Main Pool in 2005, but died before reaching maturity. This species cannot survive here, since there is no source of water that remains below ground once the pool dries up.

Rhus ovata. This particular specimen is hard to see. A black sage mostly hides it from view. There are several more prominent specimens in a short distance.

Salvia apiana X S. mellifera. This specimen is immediately next to a S. apiana of the same size, making it very easy to compare the two. Note the greenish leaves of the hybrid, compared to the whitish leaves of Salvia apiana. The leaves of the hybrid also have a different smell when rubbed. The difference is most noticeable in the inflorescence. The hybrid has the long wand of S. apiana, but the wand exhibits the typical interrupted inflorescence of S. mellifera.

I thank Jane Strong for her considerable assistance with helping me to learn the plants of the Santa Rosa Plateau, and Kay Madore, Zach Principe and Michael Charters for their sharp eyes in helping me find interesting things on this trail.

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Copyright © 2002-2006 by Tom Chester.
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Updated 19 April 2006.