Regional Distribution of the Plants on Dawson Saddle Trail

The purpose for making this chart is to see how many of the plants on the Dawson Saddle Trail, 7901' to 9134', in the San Gabriel Mountains of Los Angeles County, California, are found in other mountainous areas like the Sierra Nevada and the Rockies. This analysis was done in 2002 with the very first draft plant list for this trail. The analysis, except for the first plot, was updated in 2016 to remove four species that were on the original list, that were either misdeterminations or never found again on the trail after 2002.

The six regions used for comparison are:

regional distribution chart

Initially a separate list was made for the Rockies when that area was specifically listed by Munz. The Rockies list turned out to be no different from the list for the region outside the California Floristic Province [CA-FP], so it was combined into that list, Other NA [North America]. It was also not judicious to assume that an entry for location in a flora for Colorado was or was not part of the Rockies.

There are 49 species in this chart. This chart was not updated in 2016, so it included the four additional species mentioned above, which doesn't materially affect the chart.Of those, only one species, Peirson's lupine, Lupinus peirsonii, is unique to the San Gabriel Mountains and only one species, downy brome, Bromus tectorum, is found worldwide.

Using the updated numbers, the Transverse Ranges share 44 of the 45 species found on the Dawson Saddle Trail.

Six of these 45 shared species are found only in the Transverse Ranges, mainly the San Bernardinos, in addition to the San Gabriels. These unusual species are mostly found together on that part of the trail without shade and without trees and shrubs. The soil here is rubbly, broken up light-colored granite. This area is subject to intensive radiation, reflection and strong winds and deep cold. The list is in order seen using this page Dawson Saddle Trail Plant Guide.

The six Transverse Range endemics are:

An additional two species

are found in the Sierra Nevada excluding the rest of the CA-FP giving a total of eight exclusive to the Transverse Ranges and the Sierra Nevada. The Dawson Saddle Trail shares 34 species with the Sierra Nevada overall.

Four different species are shared with the CA-FP excluding the Sierra Nevada giving a total of ten species unique to the combined Transverse Range and Other CA-FP. These are:

The Dawson Saddle Trail has 36 species in common with other parts of the CA-FP excluding the Sierra Nevada. This is somewhat surprising since we expected to find more exclusive species shared with the Sierra Nevada than with the Other CA-FP.

Munz explains this in A Flora of Southern California on page 5 under Plant Distribution:

One would expect much similarity between our higher mountains [including the Sierra Nevada] and the Rocky Mountains and this is not so great as it might be. Undoubtedly the summer dryness of our area compared with that of the Rocky Mountains means that many northern plants, which in many cases are circumpolar and have worked their way south, have disappeared in our dry region, and have survived in the Rockies with more summer rain.

The distribution data was taken from The Jepson Manual, A California Flora and A Flora of Southern California by Munz, and Norman Weeden's A Sierra Nevada Flora. The stated distributions in these floras often are not the same, and hence different analyses may obtain slightly different lists of shared flora. Additionally, Weeden doesn't use subspecies in the Sierra. Jepson has dropped some of the data from Munz such as Arabis platysperma in the TR.

Common Name Latin Name SGM TR SN Other CA-FP Other NA Outside NA
Jeffrey pine  Pinus jeffreyi x x x x    
giant blazing star Mentzelia laevicaulis x x x x x  
rock buckwheat Eriogonum saxatile x x x x    
Grinnell's beardtongue Penstemon grinnellii var. grinnellii x x   x    
California squirreltail Elymus elymoides ssp. californicus x x x x x  
beaked penstemon Penstemon rostriflorus x x x x x  
California brickellbush Brickellia californica x x   x x  
one-seeded pussypaws Calyptridium monospermum x x x x    
silky lupine  Lupinus elatus x x        
green-leaf manzanita Arctostaphylos patula x x x x x  
Davidson's lotus Lotus nevadensis var. davidsonii x x   x    
santolina pincushion Chaenactis santolinoides x x   x    
white catch-fly Silene verecunda ssp. platyota x x x x    
white fir Abies concolor x x x x x  
sugar pine Pinus lambertiana x x x x    
mountain whitethorn Ceanothus cordulatus x x x x    
curl-leaf mountain-mahogany Cercocarpus ledifolius var. intermontanus x x x x x  
one-sided bluegrass Poa secunda ssp. secunda  x  x x x x  
Parish's needlegrass Achnatherum parishii x x x x x  
alpine sulfur-flowered buckwheat Eriogonum umbellatum var. minus x x        
pine lousewort Pedicularis semibarbata x x x x    
lodgepole pine Pinus contorta ssp. murrayana x x x x x  
wax currant Ribes cereum var. cereum x x x x x  
Burlew's onion Allium burlewii x x x      
groundsmoke Gayophytum diffusum ssp. parviflorum x x x x x  
southern alpine buckwheat Eriogonum kennedyi var. alpigenum x x        
Sierra mousetail Ivesia santolinoides x x x      
woolly mountain-parsley Oreonana vestita x x        
Peirson's lupine Lupinus peirsonii x          
snow-plant Sarcodes sanguinea x x x x    
flat-seeded rock cress Arabis platysperma x x x x x  
Tehachapi ragwort Senecio ionophyllus x x   x    
bitter root  Lewisia rediviva x x x x x  
bush chinquapin Chrysolepis sempervirens x x x x    
San Bernardino beardtongue Penstemon caesius x x x x    
pinedrops Pterospora andromedea x x x x x  
limber pine Pinus flexilis x x x x x  
Sierra gooseberry Ribes roezlii var. roezlii x x x x x  
little-leaf creambush  Holodiscus microphyllus var. microphyllus x x   x x  
spineless horsebrush Tetradymia canescens x x   x x  
mountain California-fuchsia Epilobium canum ssp. latifolium x x x x    
white hawkweed Hieracium albiflorum x x x x x  
*downy brome Bromus tectorum x x x x x x
Additional species seen [collected] by Jane on previous trips              
  Draba corrugata x x        
 white-veined wintergreen Pyrola picta x x x x x  
  Total Species 45 44 34 36 20 1
    SGM TR SN Other CA-FP Other NA Outside NA


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Updated 7 June 2016.