California Botanists are doing a better job vouchering weeds

Based on analysis of 141,500 CCH specimens of non-native plants from California, it is patently evident that we are doing a better job of vouchering weeds.  Herbarium specimens are time-consuming to collect, even more time consuming to key, label and mount, yet the graph above shows that the recent trend is upward (and, discount the actual accession rate for 2005 and beyond because of backlog of unprocessed material).  Remaining humble, we must remember that our now departed mentors of the 1930s, and departed or soon to be departed friends of the 1960s did their job well.

History of introduction of Invasive/Adventive plants in California

As a field botanists in California, I fully admit being uninterested in “weeds” early on.  So many cool. endemic plants to seek out.  Once enough experience is gained, this viewpoint fortunately changed, as it ought to, into a caution.  Invasive plant biology has become a looming problem for many regions: as a Mediterranean climate region, California is predisposed to the acquisition of adventives from other regions. 

Working recently to examine the history of non-native plant introductions into California, I downloaded >140,000 CCH database records and have begun to examine the data for pattern.  The graph above is the pattern of acquisitions: based on the first specimen record for 1506 taxa. 

The most and perhaps most important first observation I offer is this: the pace of introduction is, for all purposes, linear over time.  Contrary to the important 1993 review (post Jepson Manual Ed. 1) review of Rejmanek  (Madrono 41:161-177. 1994) the pace seems not to be neither logistic, nor slowing down.  Hope for a solution would offer that some point we would reach a saturation in exotic species richness: the bad problem is no longer getting worse.  The graph above suggests that point is not yet in view.   Trends such as this require more research least we find, that at some point, homogenization of our flora becomes too massive a problem to avoid.  If landscape-scale species richness is a zero-sum game, then we have little time to ramp up our surveillance, study and control of invasives in CA.  We best hurry up from the shape of this graph.  The overall pace 1880-2010 is about 10 plants per yr (10.3 exactly).  

Precocious flowering of ramets in Poa sierrae

Photos: top to bottom – two ramets before potting, after 130 days, respectively. Note that the ramet with a single axis is smaller than the ramet that started with three axes!!!

Poa Section Madropoa is mostly restricted to high mountains of western North America.  Poa sierrae is odd within the clade: it is characterized as being rhizomatous, dioecious and by the distinctive scaly ‘bulbils’ produced on the rhizomes.  These ramets doubtless propagate by fragmentation, so it is puzzling why P. sierrae is quite narrowly distributed.

On August 3, 2011, Poa sierrae was collected (my #21,134) at the type locality (‘Lewisia’ rock near Belden, Feather River Canyon, Plumas County, CA).  Genets were potted up quickly thereafter, and kept moist throughout the fall.  These ramets remained dormant until mid-November, when, perhaps induced by decreasing daylength, they began growth.  Growth continued modestly once the ramets responded.  After about 130 days of growth, inflorescences began to emerge. 

Precocious flowering has been reported in Poaceae: tissue-cultured bamboo can be induced to flower  (Nature Nature 344, 335 - 336, 22 March 1990).  In Arabidopsis, precocious flowering is controlled by a pair of antagonistic genes (Science Vol. 286:1960-1962. 1999).

Ordinarily, sensu Baker & Stebbins 'Genetics of Colonizing Species' one would conclude that a vegetatively spreading, precociously flowering species would be weedy.  For Poa sierra, exactly not.