Authors: Amanda Fisher
Citation: Fisher, A.E. and B. Betz. 2016. Vascular Plants of the Oasis de los Osos Reserve, San Jacinto Mountains, California. Crossosoma 42(1) 1-36.
Locality: Western edge of the Sonoran Desert, Riverside County, California (33.890060, -116.695030)
Abstract: The flora of Oasis de los Osos is an unusual assemblage of species drawn from the surrounding mountains and deserts of Southern California. The 160 acre palm oasis is a University of California Natural Reserve administered by the University of California, Riverside. The Oasis is located in the western Coachella Valley at the northwestern edge of the Sonoran Desert and on the northern slope of the San Jacinto Mountains. Botanists have visited the area since the 1890s, facilitated by the railroad route through San Gorgonio Pass, and have been intrigued by its location in a transitional zone between Sonoran Desert, Mojave Desert, montane, and South Coast floristic regions. Since the 1970s, the Oasis has been protected from development, first by the Nature Conservancy and then as a University of California Natural Reserve. Despite this long history of botanical collections and protection, there has never been a checklist published for the area. We made a comprehensive list of the vascular plants present at the Oasis by documenting the flora with our own botanical surveys and with historical collections in herbaria. We annotated the checklist with information on nativity, habit, rarity, and distribution. A total of 164 native and 24 non-native taxa were documented from the Oasis, including one rare plant, Galium angustifolium subsp. gracillimum (California Rare Plant Rank 4.2). The vegetation in the Oasis transitions from brittlebush scrub at low elevations to mixed scrub at higher elevations. Shrubs are the dominant cover type and represent 20% (38 taxa) of the plant diversity. The riparian habitat is fed by Lamb Creek, a stream that supports native fan palms, willows, cottonwoods, and a variety of herbaceous species. The Oasis flora represents an unusual mixture of taxa from the surrounding San Jacinto and San Bernardino mountains (138 taxa, 73%) and the Sonoran and Mojave Deserts (109 taxa, 58%). Invasive grasses such as brome (Bromus spp.) and Mediterranean grass (Schismus barbatus) are the dominant ground cover at lower elevations, but the other 14 invasive species we documented are not well- established. The Oasis contains a great deal of plant diversity, considering its small geographic area. We compared the Oasis flora with Deep Canyon and found that 67% of Oasis species are also present at Deep Canyon. The Oasis de los Osos is a largely intact palm oasis and canyon that is representative of the transitional floristic diversity of the western Coachella Valley.

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Families: 55
Genera: 142
Species: 184
Total Taxa (details): 185
Native Shrub, source: N. M. Fellows 42
Naturalized Annual, source: N. M. Fellows 191
Native Shrub, source: A. Fisher 266
Native Shrub, source: B. Betz 52
Native Annual, source: N. M. Fellows 139
Native Perennial, source: A. Fisher 204
Native Tree, source: A. Fisher 345
Native Shrub, source: A. Fisher 257
Native Shrub, source: A. Fisher 303
Native Perennial, source: N. M. Fellows 22
Native Perennial, source: A. Fisher 343
Native Shrub, source: A. Fisher 197
Native Shrub, source: A. Fisher 352
Native Shrub, source: N. M. Fellows 33
Native Shrub, source: A. Fisher 212
Native Shrub, source: A. Fisher 366
Native Shrub, source: N. M. Fellows 36
Invasive Annual, source: UCJR 30
Native Annual, source: B. Betz 14
Native Annual, source: June Latting
Native Perennial, source: A. Fisher 364
Native Shrub, source: N. M. Fellows 193
Native Shrub, source: B. Betz 10
Native Annual, source: A. Fisher 294
Native Perennial, source: A. Fisher 339
Native Annual, source: A. Fisher 222
Native Annual, source: Mary F. Spencer 653
Native Annual, source: A. Fisher 241
Native Annual, source: A. Fisher 238
Native Annual, source: M. L. Vincent, R. H. Swade 453
Native Perennial, source: A. Fisher 298
Naturalized Annual, source: N. M. Fellows 182
Native Annual, source: A. Fisher 332
Native Perennial, source: A. Fisher 340
Naturalized Annual, source: N. M. Fellows 174
Naturalized Annual, source: N. M. Fellows 185
Native Annual, source: N. M. Fellows 164
Native Annual, source: N. M. Fellows 130
Native Annual, source: A. Fisher 234
Native Annual, source: A. Fisher 226
Native Annual, source: N. M. Fellows 144
Native Annual, source: A. Fisher 262
Native Shrub, source: A. Fisher 210
Native Annual, source: A. Fisher 213
Native Annual, source: A. Fisher 243
Native Annual, source: N. M. Fellows 181
Native Annual, source: A. Fisher 206
Native Annual, source: A. Fisher 297
Native Annual, source: A. Fisher 207
Native Annual, source: A. Fisher 217
Native Perennial, source: A. Fisher 208
Native Annual, source: A. Fisher 229
Native Annual, source: A. C. Sanders 16286
Naturalized Annual, source: C. E. Fellows 55
Invasive Annual, source: A. Fisher 231
Invasive Annual, source: N. M. Fellows 127
Native Annual, source: A. Fisher 214
Native Perennial, source: A. Fisher 372
Native Perennial, source: B. Betz 48
Native Annual, source: N. M. Fellows 122
Naturalized Annual, source: N. M. Fellows 141
Native Shrub, source: A. Fisher 301
Naturalized Annual, source: A. Fisher 265
Native Annual, source: N. M. Fellows 194
Native Annual, source: A. Fisher 223
Native Perennial, source: B. Betz 30
Native Perennial, source: UCJR 39
Native Perennial, source: B. Betz 49
Native Perennial, source: A. Fisher 267
Native Perennial, source: N. M. Fellows 178
Native Perennial, source: A. Fisher 192
Native Perennial, source: N. M. Fellows 191
Native Shrub, source: A. Fisher 218
Native Annual, source: M. L. Vincent, R. H. Swade 454
Native Perennial, source: N. M. Fellows 63
Native Perennial, source: A. Fisher 260
Native Perennial, source: A. Fisher 282
Native Shrub, source: B. Betz 35
Native Annual, source: A. Fisher 203
Native Perennial, source: N. M. Fellows 137
Native Annual, source: N. M. Fellows 188
Native Annual, source: A. Fisher 242
Native Perennial, source: N. M. Fellows 169
Native Annual, source: N. M. Fellows 135
Native Annual, source: A. Fisher 244
Native Annual, source: N. M. Fellows 167
Native Annual, source: A. Fisher 400
Native Tree, source: A. Fisher 356
Invasive Annual, source: B. Betz 15
Native Shrub, source: A. Fisher 195
Native Perennial, source: A. Fisher 338
Native Shrub, source: N. M. Fellows 167
Native Shrub, source: A. Fisher 362
Native Shrub, source: N. M. Fellows 175
Native Annual, source: UCJR 31
Native Perennial, source: A. Fisher 355
Native Shrub, source: A. Fisher 250
Native Perennial, source: James A. Phillips 21
Native Annual, source: N. M. Fellows 146
Native Annual, source: N. M. Fellows 145
Native Annual, source: N. M. Fellows 132
Invasive Tree, source: A. Fisher 252
Native Perennial, source: A. Fisher 237
Invasive Tree, source: A. Fisher 344
Native Annual, source: A. Fisher 240
Native Annual, source: George K. Helmkamp 3081
Native Perennial, source: A. Fisher 361
Native Annual, source: A. Fisher 264
Native Perennial, source: A. Fisher 296
Native Perennial, source: Kenneth Cooper s.n.
Native Perennial, source: N. M. Fellows 136
Native Shrub, source: B. Betz 39
Native Perennial, source: June Latting s.n.
Native Perennial, source: A. Fisher 358
Native Perennial, source: B. Betz 47
Native Annual, source: Miles Fellows 143
Native Shrub, source: A. Fisher 245
Native Annual, Perennial, source: B. Betz 36
Invasive Perennial, source: A. Fisher 235
Native Annual, source: A. C. Sanders 16271
Naturalized Annual, source: N.M. Fellows 171
Invasive Annual, source: A. Fisher 255
Invasive Annual, source: N. M. Fellows 119
Native Perennial, source: A. Fisher 289
Native Perennial, source: A. Fisher 211
Native Annual, source: B. Betz 12
Native Perennial, source: N. M. Fellows 29
Native Perennial, source: N. M. Fellows 192
Invasive Perennial, source: A. Fisher 259
Native Perennial, source: N. M. Fellows 96
Invasive Annual, source: N. M. Fellows 172
Invasive Annual, source: A. Fisher 224
Invasive Annual, source: N. M. Fellows 177
Native Annual, source: N. M. Fellows 133
Native Annual, source: A. Fisher 216
Native Annual, source: A. Fisher 398
Native Perennial, source: A. Fisher 336
Native Shrub, source: A. Fisher 202
Native Shrub, source: Dick Schwenkmeyer 729
Native Annual, source: George K. Helmkamp 3075
Native Shrub, source: A. Fisher 363
Native Annual, source: N. M. Fellows 125
Native Perennial, source: N. M. Fellows 176
Native Perennial, source: A. Fisher 198; A.E. Fisher... 198 [LOB]
Native Perennial, source: A. Fisher 194
Native Perennial, source: A. Fisher 201
Native Perennial, source: A. Fisher 248
Native Liana, source: B. Betz 50
Native Perennial, source: N. M. Fellows 155
Native Perennial, source: N. M. Fellows 187
Native Shrub, source: A. Fisher 368
Native Shrub, source: A. Fisher 233
Native Tree, source: A. Fisher 193
Native Tree, source: A. Fisher 249
Native Tree, source: A. Fisher 191
Native Perennial, source: N. M. Fellows 180
Native Perennial, source: A. Fisher 205
Native Perennial, source: A. Fisher 253
Native Shrub, source: B. Betz 33
Invasive Shrub, source: A. Fisher 378
Native Perennial, source: A. Fisher 209
Native Perennial, source: A. Fisher 246
Native Perennial, source: A. Fisher 200
Invasive Tree, source: A. Fisher 399
Native Perennial, source: A. Fisher 230
Native Perennial, source: A. Fisher 199
Native Annual, source: N. M. Fellows 147
Native Shrub, source: A. Fisher 256
Native Shrub, source: B. Betz 32