Plants of Southern California: Comments On James Lightner's San Diego County Native Plants

Table of Contents

Completeness of Coverage of San Diego County Taxa
Number of Species by Family and Habit
Substantive Comments


Please read the introduction to this page first!

This delightful 2006 book is dense with information; Lightner has clearly worked hard on the book to make it as useful as possible. This second edition of his book is vastly expanded from the first edition, and is now almost a mini-Jepson Manual accessible now to the beginning botanist!

I reviewed his book for Fremontia (in press); after publication, if they grant permission, I'll reproduce my book review here.

Perhaps the most amazing thing about the book is the very high completeness of the book for common species in San Diego County. Lightner's book is an astounding 95% complete for the most common species in the County (see below).

The most critical part of the book, the accuracy of the species identifications, is quite high, since Dr. Jon Rebman, the expert on plants of San Diego County, reviewed the book. Lightner even has six accurately-identified Cryptantha species, instead of the typical Cryptantha sp. given in most such books!

However, in an essentially new book with 1,102 taxa, it would be surprising if there weren't a few items that will need revision in the next edition. The lists below resulted from a complete read-through of the entire book. The lists are separated into substantive comments and typos. Some of the typos listed here are from Lightner.

Although the list may seem long, all the comments listed here apply to an extremely-small percentage of the text. Overall, this is a very high-quality book.

A copy of the book can be ordered online from Lightner's website (no, I do not get a referral fee! This link is provided solely as a convenience.)

Lightner's website also contains a list of Modifications And Corrections To 2nd Edition.

Completeness of Coverage of San Diego County Taxa

Lightner has identified pictures of 1,023 taxa, and at least mentions how to discriminate another 79 taxa. (These numbers are not quite exact, since not every picture in the book is labeled as to species. I used my judgment as to which species were actually pictured but not labeled. It is often hard to be sure of a species from just a single picture, which is why the numbers are not exact.) The 2001 Checklist of the Vascular Plants of San Diego County by Simpson and Rebman list 2,147 total taxa. In raw numbers, Lightner thus includes a bit over 50% of all the taxa in San Diego County.

Because common species are rare; rare species are common (see How Common Are The Plants Of Southern California?), it is much more useful to ask how complete the book is for common species in the County.

To derive that figure, I took all the San Diego County lists in my database (trail guides and floras), as well as lists from the Santa Rosa Plateau and Santa Margarita Ecological Reserve, which are both adjacent or very close geographically to San Diego County. I then selected only taxa on the 2001 San Diego County Checklist as well as taxa found in Lightner that have more recent vouchers from the San Diego County Plant Atlas. I then counted the number of lists for each species, and histogrammed those numbers separately for species in or absent from Lightner's Book.

The results are shown in the following plots. The first plot below gives the raw numbers in each bin of the number of lists, showing the number found in Lightner's book and the number not found in Lightner's book as a function of the number of lists:

The plot has been truncated at 200 occurrences, and is missing a single point at # = 1 that has 643 taxa not found in Lightner's book.

The following examples will make clear what is plotted above.

First, there are a total of 74 lists used here, 54 plant trail guides and 20 floras. Thus the maximum possible number of occurrences is 74.

However, some of the lists are incomplete. For example, a trail might only have one day of fieldwork in October, and might be missing some annuals. The observed maximum number of lists for any species is 60. Two species are both found on 60 lists, redstem filaree, Erodium cicutarium; and red brome, Bromus madritensis ssp. rubens, both non-native weedy virtually-omnipresent species.

Thus the maximum number of occurrences in the plot above is set to be 60. Lightner's book contains both of the species with that number of occurrences, so the blue diamond is plotted at # of trail guides plus floras =60 with value 2. That diamond is just barely visible above the pink rectangle, plotted at 0 since there are no species with 60 occurrences that are missing from Lightner's book.

Two more examples:

For species contained on many trail guides and floras, above about 15, essentially every species is found in Lightner's book, since the pink curve almost always has a value of zero above 15. Thus above roughly 15 occurrences, Lightner's book is very highly complete. Below that point, the number of missing species begins to rise.

The curves above have the standard shape found anytime one counts the number of occurrences of species, and directly shows that common species are rare; rare species are common. There are only two species found on 60 lists, the highest number found. In comparison, 643 of the taxa are found on only a single list! This point is missing from the plot, since I truncated the vertical scale at 200 occurrences. If I had changed the scale to include this point, all the other points would have been smushed together. The lowest number for which the plot is complete is two lists, for which there are 266 taxa, 93 (35%) of which are in Lightner and 173 which are not.

The plot below converts the numbers in the previous plot to percentages, as shown above in some examples, and plots both the percentage in each occurrence bin, as well as the cumulative percentage above a given number of occurrences:

This plot is truncated below at 40%, and omits the value of 19% completeness in the bin #=1, 35% completeness in the bin #=2, and 37% completeness in the bin #=3. This truncation was done to show the variation better for the more common species.

The points in each occurrence bin shown with the pink rectangles, are the values as calculated above within each bin. The points represented with blue diamonds are calculated by taking all species found in a given bin and in all bins with higher occurrence numbers as a whole. Hence the blue diamond at a value of 15, with a value of 95%, comes from the 312 species found in Lightner's book found with an occurrence value of 15 or higher, and the 18 species not in Lightner's book also found with an occurrence value of 15 or higher.

The plot shows that the completeness is roughly 95% above 15 occurrences, and declines for rarer taxa.

The 18 species with 15 or more occurrences not found in Lightner's book are given below. I strongly suspect they will be in the next edition of the book!

#Common NameScientific NameFamily
40*prickly sow thistleSonchus asper ssp. asperAsteraceae
40pygmy-weedCrassula connataCrassulaceae
39fragrant everlastingGnaphalium canescens ssp. beneolensAsteraceae
31Pacific sanicleSanicula crassicaulisApiaceae
29branching phaceliaPhacelia ramosissima var. latifoliaHydrophyllaceae
28*rattail fescueVulpia myuros var. myurosPoaceae
27cotton-batting plantGnaphalium stramineumAsteraceae
25Vasey's prickly-pearOpuntia vaseyiCactaceae
24*common cudweedGnaphalium luteo-albumAsteraceae
19*short-fruited filareeErodium brachycarpumGeraniaceae
17seashore bentgrassAgrostis pallensPoaceae
16*hedge parsleyTorilis nodosaApiaceae
16prickly cryptanthaCryptantha muricataBoraginaceae
16chick lupineLupinus microcarpus var. microcarpusFabaceae
16minute-flowered cryptanthaCryptantha micromeresBoraginaceae
15Pomona locoweedAstragalus pomonensisFabaceae
15black-hair nettleHesperocnide tenellaUrticaceae
15knot grassPaspalum distichumPoaceae

It may not be a coincidence that Gnaphalium luteo-album was also missing from Beauchamp (1986).

Although Gnaphalium stramineum is listed as being in the book, it is actually misidentified. In contrast, Gnaphalium canescens ssp. beneolens is actually in the book, but it is labeled Gnaphalium canescens ssp. microcephalum (see below for more details on both).

Number of Species by Family and Habit

Of the 1,102 taxa in Lightner's book, 286 of them are shrubs or trees and 816 are herbs. These numbers are broken down by Jepson Manual family (not the updated families used in the book) in the second table below.

The first table below gives the most common families by total number of taxa. All 28 families with 10 or more taxa in the book are listed, which contain 79% of all the taxa in the book. The other 21% of all taxa in the book are contained in 83 families.

Nearly one-quarter of all taxa are found in just two easy-to-recognize families, the Asteraceae and Fabaceae. Half of all taxa in the book are found in just nine families, which is typical of Southern California floras. Thus any reader that can identify those nine families can immediately restrict the search for an unknown species to a small subset of the entire book.

In the following, I have used Lightner's classification for habit. See below for additional information.

Families with 10 or more taxa in the book

JM Family# shrubs/trees# herbsTotal Per FamilyCumulative % of All Taxa
Brassicaceae 424234%
Polemoniaceae 353544%
Onagraceae 313147%
Cactaceae21 2158%
Rhamnaceae17 1765%
Apiaceae 161667%
Boraginaceae 161668%
Caryophyllaceae 151571%
Cyperaceae 141472%
Pteridaceae 131375%
Ericaceae11 1176%
Nyctaginaceae 111177%
Ranunculaceae 111178%
Fagaceae10 1079%

Complete list of families

JM Family# shrubs/trees# herbsTotal
Acanthaceae1 1
Aceraceae1 1
Aizoaceae 55
Amaranthaceae 66
Anacardiaceae7 7
Apiaceae 1616
Apocynaceae 11
Arecaceae3 3
Asclepiadaceae 66
Bataceae 11
Berberidaceae3 3
Betulaceae1 1
Bignoniaceae1 1
Blechnaceae 11
Boraginaceae 1616
Brassicaceae 4242
Burseraceae1 1
Cactaceae21 21
Campanulaceae 66
Cannabaceae 11
Caprifoliaceae4 4
Caryophyllaceae 1515
Celastraceae1 1
Convolvulaceae 88
Cornaceae2 2
Crassulaceae 88
Cucurbitaceae 33
Cupressaceae4 4
Cuscutaceae 22
Cyperaceae 1414
Datiscaceae 11
Dennstaedtiaceae 11
Dipsacaceae 11
Dryopteridaceae 22
Ephedraceae3 3
Equisetaceae 33
Ericaceae11 11
Fagaceae10 10
Fouquieriaceae1 1
Frankeniaceae 11
Garryaceae2 2
Gentianaceae 22
Geraniaceae 66
Grossulariaceae8 8
Iridaceae 22
Juglandaceae1 1
Juncaceae 99
Krameriaceae2 2
Lauraceae1 1
Limnanthaceae 11
Linaceae 33
Lythraceae 22
Marsileaceae 11
Myoporaceae1 1
Myrtaceae3 3
Nyctaginaceae 1111
Oleaceae2 2
Onagraceae 3131
Orchidaceae 11
Orobanchaceae 11
Oxalidaceae 33
Paeoniaceae 11
Pinaceae9 9
Plantaginaceae 55
Platanaceae1 1
Plumbaginaceae 33
Polemoniaceae 3535
Polypodiaceae 11
Portulacaceae 99
Primulaceae 22
Pteridaceae 1313
Ranunculaceae 1111
Rhamnaceae17 17
Rubiaceae 66
Rutaceae2 2
Salicaceae7 7
Saururaceae 11
Saxifragaceae 55
Selaginellaceae 11
Simaroubaceae1 1
Simmondsiaceae1 1
Styracaceae1 1
Tamaricaceae3 3
Tropaeolaceae 11
Typhaceae 22
Urticaceae 22
Verbenaceae 11
Violaceae 44
Viscaceae4 4
Vitaceae1 1
Zosteraceae 33

Substantive Comments

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Copyright © 2006 by Tom Chester
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Last update: 1 March 2006