10 June Nature Paper: Substantial Underestimate of Extinct Plants in California

Extinction Density of World Flora

Humphreys et al (2019) compiled a global roster of presumed extinct seed plants.  Their assessment (based on their Supplementary Data 1 spreadsheet) tallies but 9 plants as being extinct in California.  This is incorrect: CNPS (2019) records 22 presumed extinct plants (all seed plants).   No presumed extinct plants have been rediscovered in California since 2001 (CNPS 2019), hence this number is considered factually correct as compared to the Humphreys et al (2019) tally.  The Humphreys et al (2019) tally used as sources CPS (1990) and Kartesz (1994), but not (CNPS 2019).  Unfortunately, Humphreys et al (2019) thusly underestimate the magnitude of extinction in the California Floristic Province.

Humphreys et al (2019) did not base their regional extinction ranking based on area:  correcting for this (the table below), California has the 3^rd highest rate, and their Fig. 1 does not reflect this.   Moreover (see the table) the 22 presumed extinct plants in California equals or exceeds the putative highest ranked regions given by Humphreys et al (2019).   Unfortunately, the underestimate for California is consequential, as the Humphreys et al (2019) assessment is re-tweeted (e.g. Ledford 2019) giving the incorrect rankings and doubtless will receive wide distribution.  

Thusly, California and the Cape Province (S. Africa) have similar magnitudes of plant extinction density.

Extinction Density Tabulation

Country	Area (km2)	Extinctions	Extinction Density (km2/extinction)	Global Rank
Hawaii	28311	79	3145	1st
Cape Province	298428	37	8065	2nd
California	423970	22	19271	3rd
Western Australia	2645615	22	120225	4th
India	3287263	20	164363	5th

Humphreys et al (2019) quite correctly point out that many presumed extinct plants have at some point been rediscovered, and this is certainly true for California (the second table below).  Clearly on theoretical grounds (Preston 1948) it is impossible to determine when a plant can be deemed extinct hence it is not unexpected that over time, and 29 California plants have been ‘rediscovered’. 

Presumed Extinct Plants in California

Date/Inventory Edition	Reference	No. Extinct Plants
1980 2nd Edition	Smith et al. (1980)	44
1984 3rd Edition	Smith & York (1984)	34
1988 4th Edition	Smith & Berg (1988)	39
1994 5th Edition	Skinner & Pavlick (1994)	34
2001 6th Edition	Tibor (2001)	29
2009 Electronic Inventory	CNPS (2019)	22

References Cited

California Native Plant Society, Rare Plant Program. 2019. Inventory of Rare and Endangered Plants of California (online edition, v8-03 0.39). Website http://www.rareplants.cnps.org [accessed 13 June 2019].

Center for Plant Conservation (1990). Centre for plant conservation data for North American plants database. CPC, Centre for plant conservation.

Humphreys A.M., R. Govaerts, S.Z. Ficinski, E.N. Lughadha and M.S. Vorontsova  2019. Global dataset shows geography and life form predict modern plant extinction and rediscovery  Nature Ecology & Evolution. https://doi.org/10.1038/s41559-019-0906-2

Kartesz, J.T. (1994) A synonymized checklist of the vascular flora of the United States, Canada, and Greenland. 2nd edition. 2 vols. Timber Press, Portland.

Ledford, H.  2019. Global plant extinctions mapped,  Nature 570:148-149.

Preston, F. W. 1948. The commonness, and rarity, of species. Ecology 29(3): 254-283.

Skinner, M.W. and B.M. Pavlick. 1994. Tibor, D.  [ed.] 2001.  Inventory of Rare and Endangered Plants of California, fifth edition.  California Native Plant Society, Sacramento, CA.

Smith, J.P. Jr., R.J. Cole, J.0. Sawyer, Jr.  and W.R. Powell.  1980. Inventory of Rare and Endangered Plants of California, second edition.  California Native Plant Society, Sacramento, CA.

Smith, J.P. Jr. and R. York.  1984. Inventory of Rare and Endangered Plants of California, third edition.  California Native Plant Society, Sacramento, CA.

Smith, J.P. Jr. and K. Berg.  1988. Inventory of Rare and Endangered Plants of California, fourth edition.  California Native Plant Society, Sacramento, CA.

Tibor, D.  [ed.] 2001.  Inventory of Rare and Endangered Plants of California, sixth edition.  California Native Plant Society, Sacramento, CA.

Note:

Humphreys et al (2019) Supplemental  Data 1 lists Atriplex tularensis as rediscovered, which is incorrectl.