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":

• The taxa with the largest absolutely number of plants, regardless of how widely-distributed those taxa may be;

• The taxa with the widest distribution in Southern California, and hence are most likely to be found on a random trail; or

• The taxa with the highest combination of the above two characteristics, after weighting the two characteristics in some way.

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:

Title	Meaning
#all	number of all trails and floras in the database that contain this taxon (52 maximum)
#muns	number of floras by Bob Muns in the database that contain this taxon (13 maximum)
#floras	number of all floras in the database that contain this taxon (19 maximum)
#trails	number 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 Name	Common Name	Family	#all	#muns	#floras	#trails
Malosma laurina	laurel sumac	Anacardiaceae	27	9	13	14
Toxicodendron diversilobum	poison oak	Anacardiaceae	28	11	14	14
Ambrosia psilostachya	western ragweed	Asteraceae	26	10	13	13
Artemisia californica	California sagebrush	Asteraceae	33	11	15	18
Artemisia douglasiana	mugwort	Asteraceae	26	11	14	12
Baccharis salicifolia	mule fat	Asteraceae	29	11	14	15
Brickellia californica	California brickellbush	Asteraceae	26	9	13	13
Centaurea melitensis	*tocalote	Asteraceae	32	12	16	16
Erigeron foliosus	leafy daisy	Asteraceae	12	9	10	2
Erigeron foliosus var. foliosus	leafy daisy	Asteraceae	15	0	3	12
Eriophyllum confertiflorum	golden yarrow	Asteraceae	15	10	11	4
Eriophyllum confertiflorum var. confertiflorum	golden yarrow	Asteraceae	21	0	5	16
Gnaphalium californicum	California everlasting	Asteraceae	27	11	15	12
Gnaphalium canescens ssp. microcephalum	white everlasting	Asteraceae	28	10	13	15
Hazardia squarrosa	saw-toothed goldenbush	Asteraceae	9	9	8	1
Hazardia squarrosa var. grindelioides	saw-toothed goldenbush	Asteraceae	18	0	4	14
Heterotheca grandiflora	telegraph weed	Asteraceae	29	11	15	14
Lessingia filaginifolia	California-aster	Asteraceae	10	9	8	2
Lessingia filaginifolia var. filaginifolia	California-aster	Asteraceae	26	2	7	19
Hirschfeldia incana	*shortpod mustard	Brassicaceae	31	12	15	16
Lonicera subspicata	southern honeysuckle	Caprifoliaceae	6	8	6	0
Lonicera subspicata var. denudata	southern honeysuckle	Caprifoliaceae	20	0	5	15
Sambucus mexicana	blue elderberry	Caprifoliaceae	34	12	17	17
Salsola tragus	*Russian thistle	Chenopodiaceae	28	11	14	14
Marah macrocarpus	wild-cucumber	Cucurbitaceae	12	11	12	0
Marah macrocarpus var. macrocarpus	wild-cucumber	Cucurbitaceae	14	0	3	11
Lotus scoparius	deerweed	Fabaceae	17	11	11	6
Lotus scoparius var. scoparius	deerweed	Fabaceae	13	0	4	9
Quercus agrifolia	coast live oak	Fagaceae	10	9	10	0
Quercus agrifolia var. agrifolia	coast live oak	Fagaceae	18	0	3	15
Erodium cicutarium	*redstem filaree	Geraniaceae	27	12	16	11
Marrubium vulgare	*horehound	Lamiaceae	26	12	15	11
Salvia apiana	white sage	Lamiaceae	27	8	12	15
Salvia mellifera	black sage	Lamiaceae	30	10	14	16
Epilobium canum	California fuchsia	Onagraceae	10	8	7	3
Epilobium canum ssp. canum	California fuchsia	Onagraceae	16	6	10	6
Epilobium canum ssp. latifolium	mountain California-fuchsia	Onagraceae	10	2	5	5
Eriogonum fasciculatum	California buckwheat	Polygonaceae	10	11	10	0
Eriogonum fasciculatum var. foliolosum	California buckwheat	Polygonaceae	23	0	4	19
Eriogonum fasciculatum var. polifolium	California buckwheat	Polygonaceae	13	0	2	11
Rhamnus ilicifolia	hollyleaf redberry	Rhamnaceae	30	9	14	16
Adenostoma fasciculatum	chamise	Rosaceae	28	9	13	15
Heteromeles arbutifolia	toyon	Rosaceae	33	10	14	19
Salix lasiolepis	arroyo willow	Salicaceae	29	9	14	15
Mimulus aurantiacus	bush monkeyflower	Scrophulariaceae	29	10	12	17
Avena barbata	*slender wild oats	Poaceae	24	11	15	9
Avena fatua	*wild oats	Poaceae	18	11	14	4
Bromus diandrus	*ripgut brome	Poaceae	33	12	16	17
Bromus hordeaceus	*soft chess	Poaceae	26	11	15	11
Bromus madritensis ssp. rubens	*red brome	Poaceae	29	11	13	16
Melica imperfecta	small-flowered melica	Poaceae	26	10	14	12

Go to:

• How Common Are The Plants Of Southern California?
• Native and Introduced Plants of Southern California