The revised Jepson Manual gives me the view that we have a even stronger picture of the endemic and native flora of California than the first 1993 edition. By contrast, the new Manual shows me that we have a primitive or no clue as to where the invasive flora is trending.
Based on an ongoing comparison of Calflora, taxa in TJM2 and JPF categories for waifs, garden weeds etc, and CCH specimen records, I find there is about a 1/3 correspondence. TJM2 treats about 1207 ‘established’ exotics ; 296 ‘waifs; 130 ‘garden weeds’; 72 ‘cultivated’ –1705 taxa total. By contrast, CALFLORA has about 800 more names for non-natives! Circa. 300 species are in CCH that rare not in Index to California Plant Names Current Status Categories. Preliminary perusal of the CCH and the CALFLORA rosters clearly indicate to me that a sizeable number of cultivated, ornamentals have records in one or the other database.
Which cultivated plants are risks? Essentially, horticulture in California, with emphasis rightly on drought-tolerance, provides an ongoing infection pressure. More and more new plants are offered each season, more and more some minor proportion of these might be the next Genista. How to moderate this threat?
One thing that merits consideration is what, in Hawaii, is a Invasive Assessment Protocol, along the lines of Hawaii Exotic Plant Evaluation Protocol (Daehler et al 2004). Color code the system; require labels in garden centers to bear symbols for invasive potential.
Given the native flora of California is 6600 or so taxa, given the non-native flora, some 2000± more taxa, and given that there are probably an ±3000-4000 (or larger?) number of cultivated, Mediterranean or temperate-origin plants in the trade in CA, the risk of not progressing in this arena is significant.
Daehler, C. C., J. S. Denslow, S. Ansari, and H. Kuo. 2004. A risk assessment system for screening out
invasive pest plants from Hawai'i and other Pacific Islands. Conservation Biology 18:360-368.