here is the calculus I use:
1. there are on the order of 450,000 species of vascular plants
2. perhaps half of those are adapted to places that are too warm or too cold to grow in California, that leaves 225,000
3. let us for sake of sanity, cut 225,000 in half and we will sleep better
4. in California we have ca. 2000 non native plants and 7000 natives, total ca. 9000
5. Subtract 9000 from 125,000 and we get 116,000 plants that might some day come hither
6. the challenge of introductions is daunting. Which become invasive, if only 1% of those might be invasive, that is far too many: amongst the 1160 of the 1% there are going to be a host of horror stories. Halloween and botany do not mix well (except for the requirement of fully ripe pepos). Early detection and eradication is the most economical solution to the problem. Detect the zebra mussel early – after all it had stripes – and you save a bundle. Fail to provide botanists whom can make detections, fail to allow the detection botanists to roam, and you guarantee the next star-thistle will be on our doorstep.
The problem seems daunting but daunting problems are a fun element of challenge.