The Most Common Plants of Southern California

As of 8 November 2002, we have 52 trails and floras (lists for short in the following) in our Master List. We thought it would be fun to see which are the most common taxa. (See How Common Are The Plants Of Southern California? for histograms of the number of occurrences for all the taxa in our Master List.)

Note that there are many ways to define the "most common taxa":

Some taxa satisfy all of the above, such as chamise, Adenostoma fasciculatum, which is both widely distributed and abundant in most of its occurrences. Some taxa satisfy only one criterion. Goldfields, Lasthenia californica, often has a very large number of individual plants, but is not found on most trails. In contrast, laurel sumac, Malosma laurina, is widely distributed, and is found on most trails, but never with the large number of plants of chamise or goldfields.

In the future, we'll be able to quantify occurrences much better from our estimates of the abundance of each species along each trail. For now, we simply select the taxa which appear most frequently on the lists in our Master List. This selects species like laurel sumac in preference to species like goldfields.

Caveat: This is only a preliminary, just-for-fun list. This list will change as the trail guides become more complete. In particular, this list is incomplete for annuals due to the severe drought in 2002.

We arbitrarily selected all species that were found on at least half, 26, of the 52 lists. In addition, we manually added species that had 26 observations when a subspecies was combined with the species, since in many of the lists, a subspecies was not identified. We kept these taxa separate, since it is not possible to combine the observations without going back to the individual lists. We did not perform an exhaustive check for all such species, so that part of the list may also be incomplete. We have color-coded the separate taxa in the table that are a single species. Finally, even though neither species of wild oats were found on at least 26 lists, we included them to the table below, since many of the lists only have Avena sp. on them. Most of these should receive a species identification next spring. There is little doubt that both of the wild oats species will make this table when they are identified on those lists.

The table is presented in family order. Although the numbers are given for how many times each taxa was observed, the differences between those numbers are mostly not statistically significant. That is, if we produced a table sorted in order of commonness as of now, with 52 lists, and produced another table later with 60 lists, the species will not be found in the same order. We need well over 100 lists to begin to produce an ordered table that would be truly representative of the actual frequency in Nature.

There are at least two statistical effects which affect the observed number of occurrences:

  1. the randomness as to whether a given species actually occurs on a trail, even if the species is present in a given area. For example, laurel sumac, Malosma laurina, is spottily distributed in many areas. Some trails will not contain a laurel sumac simply because none of the plants in that area occurred on the location of the trail itself.

  2. the randomness of the location of the next trails we add to our Master List. If we add trails in areas where laurel sumacs are not found, for example at higher altitude, laurel sumac will fall behind other species found on those trails.

Thus although the differences between the observed occurrence numbers are not statistically significant now, there is no doubt that all of the species in this table are very common plants. Any list of common species would include all of these species. For comparison, the most frequent number of occurrences for all species in our Master List is ONE, which is way below the threshold here of 26! Most species in our Master List occur on only a single trail or on only a few trails. No matter how many lists we add to our Master List, none of the species with an occurrence number of one or two will ever come close to being found on half of our lists.

The numbers presented in the table below are:

#allnumber of all trails and floras in the database that contain this taxon (52 maximum)
#munsnumber of floras by Bob Muns in the database that contain this taxon (13 maximum)
#florasnumber of all floras in the database that contain this taxon (19 maximum)
#trailsnumber of our trails that contain this taxon (33 maximum)

There are 39 total species in the following table, of which 10 are non-natives, 26% of the total. This is higher than the percentage of non-natives in the total California flora, 17% (1023 non-natives out of a California flora of 5867 species, using the Jepson Manual numbers). This is simply due to the advantage that non-native taxa have in competing with native taxa.

Remember, this table is just-for-fun now. We'll make a proper list in the future when our trail guides are more complete.

For those of you who just cannot resist sorting these species in order of occurrences, here it is.

Latin NameCommon NameFamily#all#muns#floras#trails
Malosma laurinalaurel sumacAnacardiaceae2791314
Toxicodendron diversilobumpoison oakAnacardiaceae28111414
Ambrosia psilostachyawestern ragweedAsteraceae26101313
Artemisia californicaCalifornia sagebrushAsteraceae33111518
Artemisia douglasianamugwortAsteraceae26111412
Baccharis salicifoliamule fatAsteraceae29111415
Brickellia californicaCalifornia brickellbushAsteraceae2691313
Centaurea melitensis*tocaloteAsteraceae32121616
Erigeron foliosusleafy daisyAsteraceae129102
Erigeron foliosus var. foliosusleafy daisyAsteraceae150312
Eriophyllum confertiflorumgolden yarrowAsteraceae1510114
Eriophyllum confertiflorum var. confertiflorumgolden yarrowAsteraceae210516
Gnaphalium californicumCalifornia everlastingAsteraceae27111512
Gnaphalium canescens ssp. microcephalumwhite everlastingAsteraceae28101315
Hazardia squarrosasaw-toothed goldenbushAsteraceae9981
Hazardia squarrosa var. grindelioidessaw-toothed goldenbushAsteraceae180414
Heterotheca grandifloratelegraph weedAsteraceae29111514
Lessingia filaginifoliaCalifornia-asterAsteraceae10982
Lessingia filaginifolia var. filaginifoliaCalifornia-asterAsteraceae262719
Hirschfeldia incana*shortpod mustardBrassicaceae31121516
Lonicera subspicatasouthern honeysuckleCaprifoliaceae6860
Lonicera subspicata var. denudatasouthern honeysuckleCaprifoliaceae200515
Sambucus mexicanablue elderberryCaprifoliaceae34121717
Salsola tragus*Russian thistleChenopodiaceae28111414
Marah macrocarpuswild-cucumberCucurbitaceae1211120
Marah macrocarpus var. macrocarpuswild-cucumberCucurbitaceae140311
Lotus scopariusdeerweedFabaceae1711116
Lotus scoparius var. scopariusdeerweedFabaceae13049
Quercus agrifoliacoast live oakFagaceae109100
Quercus agrifolia var. agrifoliacoast live oakFagaceae180315
Erodium cicutarium*redstem filareeGeraniaceae27121611
Marrubium vulgare*horehoundLamiaceae26121511
Salvia apianawhite sageLamiaceae2781215
Salvia melliferablack sageLamiaceae30101416
Epilobium canumCalifornia fuchsiaOnagraceae10873
Epilobium canum ssp. canumCalifornia fuchsiaOnagraceae166106
Epilobium canum ssp. latifoliummountain California-fuchsiaOnagraceae10255
Eriogonum fasciculatumCalifornia buckwheatPolygonaceae1011100
Eriogonum fasciculatum var. foliolosumCalifornia buckwheatPolygonaceae230419
Eriogonum fasciculatum var. polifoliumCalifornia buckwheatPolygonaceae130211
Rhamnus ilicifoliahollyleaf redberryRhamnaceae3091416
Adenostoma fasciculatumchamiseRosaceae2891315
Heteromeles arbutifoliatoyonRosaceae33101419
Salix lasiolepisarroyo willowSalicaceae2991415
Mimulus aurantiacusbush monkeyflowerScrophulariaceae29101217
Avena barbata*slender wild oatsPoaceae2411159
Avena fatua*wild oatsPoaceae1811144
Bromus diandrus*ripgut bromePoaceae33121617
Bromus hordeaceus*soft chessPoaceae26111511
Bromus madritensis ssp. rubens*red bromePoaceae29111316
Melica imperfectasmall-flowered melicaPoaceae26101412

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Copyright © 2002 by Tom Chester and Jane Strong
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Last update: 24 November 2002