504 
serrulata, lva xanthifolia, Xanthium commune, Ambrosia spp., Helian- | 
thus spp. A few introduced plants have come to Colorado from 
tropical America, as Amarantus graecizens and Datura altho 
Summary. There are 95 species of European plants growing 
without cultivation in Colorado. Of these, 26 are garden-escape 
while the rest have been introduced in various ways. The species 
are found to be distributed in 26 natural families; those best 
represented are the following: Gramineae 21 species, Polya 
naceae 8 species, Cruciferae 11 species, Compositae 10 species. 
The four families just named contain more than half of all the 
species. A short discus-— 
eC sion of the geography and 
ge climate shows the region — 
A well adapted to receive 
‘i > Os. immigrant species in the 
r Brg she lower and moderate alti- | 
we - a tudes. Most of the intro-— 
i fat ery f | duced plants are confined — 
i Sime f to the plains area and 
ZZ SAC rT My foothill zone, a few are 
41Y PSR found in the montane 
. i zone, practically none at — 
. all in the sub-alpine and 
: ba ‘es alpine zones. The conti- 
# nental divide has no in- 
fluence in determining 
Map of North America showing the location of Colorado tHe introduction of plants 
Sinton) The high cities of ore shown by thetmet 10M a distance. Except 
flowing away in all directions. for such plants as dande- 
lion, shepherd’s purse, 
knotgrass and mallow (Zarazacum tarazacum, Bursa bursa pastoris, 
Polygonum aviculare and Malva rotundifolia) the ruderal plants 
in Colorado most abundant in individuals are not of European 
origin, but natives of the region. 
