Saturday, July 20, 2019

Enumerating California Needlegrasses (the tribe Stipeae)

Peterson PM, Romaschenko K, Soreng RJ, Reyna JV (2019) A key to the North American genera of Stipeae (Poaceae, Pooideae) with descriptions and taxonomic names for species of Eriocoma, Neotrinia, Oloptum, and five new genera: Barkworthia, ×Eriosella, Pseudoeriocoma, Ptilagrostiella, and Thorneochloa. PhytoKeys 126: 89–125. https://doi. org/10.3897/phytokeys.126.34096

California has by my count 42 taxa of needlegrasses: the Tribe Stipeae Dumort.  In the Jepson Manual, a broad (and overly simplified) generic concept was used: a single genus Stipa L.  Robustly supported phylogenetic and biogeographic data now indicates that a number of lineages qualify as genera, based on globally coherent viewpoint (yes, in Jepson-ease its so easy to just blurt out Stipa! and remain in ignorance).  Botanists struggle with the concept of a genus, and are, when confused, inclined to combine lineages and they don’t know when to stop.  This results inappropriate and ill-informative treatments: one could recognize only Triticum L. for all species within the Triticeae, the cereal grasses, decidedly poor science, and a setback for bread baking!  

Our generic lineup thus becomes (new named genera are bold italics):

The California roster: Format New Name             STATUS
Amelichloa brachychaeta (Godr.) Arriaga & Barkworth    Native
Amelichloa caudata (Trin.) Arriaga & Barkworth Waif
Amelichloa clandestina (Hack.) Arriaga & Barkworth         Waif
Ampelodesmos mauritanica (Poir.) T. Durand & Schinz,   Naturalized
Barkworthia stillmanii (Bol.) Romasch., P.M. Peterson & Soreng  Native
Eriocoma arida (M.E. Jones) Romasch.    Native
Eriocoma bloomeri (Bol.) Romasch.          Native
Eriocoma coronata (Thurb.) Romasch.    Native
Eriocoma hymenoides (Roem. & Schult.) Rydb.   Native
Eriocoma latiglumis (Swallen) Romasch. Native
Eriocoma lemmonii (Vasey) Romasch.    Native
Eriocoma lemmonii subsp. pubescens (Crampton) Romasch.        Native
Eriocoma lettermanii (Vasey) Romasch. Native
Eriocoma nelsonii (Scribn.) Romasch. subsp. dorei (Barkworth & J. Maze) Romasch.           Native
Eriocoma nevadensis (B.L. Johnson) Romasch.    Native
Eriocoma occidentalis  (Thurb. ex S. Watson) Romasch. subsp. californica (Merr. & Burtt Davy) Romasch. Native
Eriocoma occidentalis (Thurb. ex S. Watson) Romasch. ssp. occidentalis   Native
Eriocoma occidentalis (Thurb. ex S. Watson) Romasch. subsp. pubescens (Vasey) Romasch.,          Native
Eriocoma parishii (Vasey) Romasch.         Native
Eriocoma pinetorum (M.E. Jones) Romasch.         Native
Eriocoma thurberiana (Piper) Romasch. Native
Eriocoma webberi Thurb.             Native
Hesperostipa comata (Trin. & Rupr.) Barkworth subsp. comata    Native
Hesperostipa comata subsp. intermedia (Scribn. & Tweedy) Barkworth   Native
Jarava plumosa (Spreng.) S.W.L. Jacobs & J. Everett          Waif
Nassella cernua (Stebb. & Löve) Barkworth           Native
Nassella formicara (Del.) Barkworth         Native
Nassella lepida (A. Hitchc.) Barkworth     Native
Nassella manicata (E. Desv.) Barkworth  Naturalized
Nassella pulchra (A. Hitchc.) Barkworth  Native
Nassella tenuissima (Trin.) Barkworth     Waif
Nassella viridula (Trin.) Barkworth            Native
Oloptum miliaceum (L.) Röser & H.R. Hamasha   Naturalized
Oryzopsis exigua Thurb. Native
Oryzopsis micrantha (Trin. & Rupr.) Thurb.           Native
Pappostipa speciosa (Trin. & Rupr.) Romaschenko             Native
Piptatherum miliaceum (L.) Coss.              Naturalized
Piptochaetium setosum (Trin.) Arechav. Naturalized
Piptochaetium stipoides (Trin. & Rupr.) Hack. ex Arechav.              Naturalized
Ptilagrostiella kingii (Bol.) Romasch.         Native
Stipellula capensis (Thunb.) Röser & H.R. Hamasha            Naturalized
Thorneochloa diegoensis (Swallen) Romasch.      Native

Wednesday, July 3, 2019

Typification of Phacelia vallicola Congdon ex Brand

This basionym was published in Konigliches Gymnasium zu Sorau, Beilage zum Jahresbericht. Sorau 7. 1911.  The protologue is apparently not available on line (accessed 7/2/2019).  Brand (1913) and Jepson (1943) cite the holotype as “Hites Cove, J.W. Congdon, 8 May 1892”.    Brand (1913) cited only one specimen as “Parish”. 

Two Congdon specimens database on line bear this date: UC126012 is a specimen that was originally part of the Brandegee Herbarium (Carter 2011), acquired afterwards by UC Berkeley.  A second specimen, DS134418 is labeled as an isotype.   Parish's herbarium was sold to Stanford University in 1917, and for this reason the specimen CAS BOT-BC6817| DS 134418 is the probable holotype, and the UC specimen is an isotype. 

Brand specifically cited three other specimens as “n 126001 u 133062 in Herb Berkeley”, and “ud bei Hennessey Ranch (Lembert, Mai 1984, Herb Berkeley)”. UC126001 and UC133062 are Congdon specimens collected at Hites Cove, Mariposa County on May 29, 12898 and are not type material.  There are two accessions of a Lembert specimen from Hennessey Ranch (vicinity present day El Portal, Mariposa County: UC107446 and UC24328.  These too are not type material.

Phacelia vallicola was poorly collected until the 1980s, and its range imperfectly known (Bowcutt 1989).  At the time, it was judged a rare plant and was considered of conservation concern (Smith & York 1984) but was later dropped as being too common.

JStore Plant Science search on Phacelia vallicola yields a set of specimens under the name Phacelia vallicola Heller.  This name was never published: the specimens, NDG42076, K001096033 and  PH00028311.  The specimens are Phacelia hastata Lehm. var. charlestonensis Cronq. (Niles & Leary 2007)

Bowcutt, F. 1989. Reappraisal of the range of Phacelia vallicola (Hydrophyllaceae).  Madroño 36(1):51-52.

Brand, A.  1913. Hydrophyllaceae, in Engler Das Pflanzenreich, IV. 251. 29-57.

Carter, N. C. 2011. The Brandegees: leading botanists in San Diego. Journal of California Garden & Landscape History Society 14: 1-9.

Jepson, W.L.  1943.  Hydrophyllaceae, Pp. 223-297 in A Flora of California, Jepson Herbarium, University of California, Berkeley. 

Niles, W.E. and P.J. Leary.  Annotated checklist of the vascular plants of the Spring Mountains Clark and Nye Counties, Nevada.  Mentzelia (J. Nevada Native Plant Society) Vol. 8

Smith, J.P and R. York.  1984.  Inventory of rare and endangered plants of California.  California Native Plant Society, Sacramento, CA.

Thursday, June 13, 2019

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 3rd 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
Area (km2)
Extinction Density
Cape Province
Western Australia

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

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 [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.
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.

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

Monday, April 16, 2018

Resurrect Mahonia sonnei!

Mahonia sonnei was named by Abrams (1934) based on a single gathering from Truckee, California.  The syntype specimens were collected by Charles F. Sonne in August 1884 and again in April 1885 (no lectotype has been as yet designated). 

McMinn pigeon-holed M. sonnei in Berberis (McMinn 1939), as was then and still recently the custom.  We now know that Mahonia is a distinct genus well separated from Berberis, and from the related genera Alloberberis and Moranothamnus in both Asia and the New World (Yu and Chung 2017).

Poor Mahona sonnei: it has died twice.

First it disappeared for 90 years: the species was never collected again until 1973 when James B. Roof and members of the California Native Plant Society organized the founding “rare plant treasure hunt” (Roof 1974).

Mahonia sonnei was listed under the U.S. Endangered Species Act of 1973 in(Federal Register 44, p. 64246, 6 November 6 1979.  In 1993, Michael Williams placed it in synonymy in the first edition of the Jepson Manual (Williams 1993), where it has remained ever since (Williams 2012, Whittemore 1997).  Then it disappeared again - Mahonia repens was delisted – officially removed from the Endangered Species Act in 2003.  Poof!  The delisting was directly a result of a floristic treatment, not a detailed published study.

Abrams (1934) and McMinn (1939) keyed M. sonnei thusly:
Mahonia sonnei: Leaflets bright-green and shining above, teeth 12-16 on each margin, merely bristle-tipped; lower surface not gray
           Mahonia repens: Leaflets dull above; teeth small, bristle-tipped, usually 12 on a side.

In revisiting the Berberidaceae of California, I reviewed Abrams’ original description, and now that we have a wealth of imaged herbarium specimens, sought to do a quick, simple test of the number of  teeth per side of a leaflet.  Marginal teeth were counted on the 3 of the 4 syntype specimens of M. sonnei (NDG19699, US2699, DS95828), and from 70 specimens selected throughout the geographic range of M. repens (Fig. 2)

Figure 1 shows a box plot of the results: M. sonnei averages 15.9 teeth per leaflet side, while M repens averaged 10.2.  The difference is significant at p=<0 .0001="" df="68).<span" style="mso-spacerun: yes;"> 
Imaged specimens of M. repens were selected from throughout its wide range in western North America (Figure 2).

Figure 1.  Box plot of number of teeth on one side of leaflets from 3 of 4 syntypes M. sonnei and from 70 randomly chosen specimens of M. repens.  The difference in means is highly significant (T-test)

Figure 2.  Geographic distribution of M. repens, based on specimens served up on SEINet

This simple comparison suggests that M. sonnei and M. repens exhibit different leaf morphometrics.  Mahonia sonnei has never been DNA sequenced.  My inspection of specimens so far suggests that, overall, M. repens and the syntype specimens M. sonnei occupy differing leaf trait morphometric multivariate space (compare Fig. 3 and Fig. 4).  Additional work on this problem is planned: the expectation is that substantial morphometric differences between M. sonnei and M. repens can be demonstrated.  However, M. sonnei needs to be sequenced.

Figure 3 and 4.  Representative leaflets of M. sonnei (below) and M. repens (above, the leaflet chosen based on the observed mean of n=10 teeth)

Preliminary conclusion: Mahonia sonnei is a distinct taxon.  The baby was thrown out with the bathwater.

Literature Cited

Abrams, Leroy.  1934.  The Mahonias of the Pacific States.  Phytologia 1(2):89-94.
McMinn, Howard E.  1939.  An Illustrated Manual of California Shrubs.  Univ. of California Press, Berkeley, CA
Roof, J.B.  1974.  Found alive: the Truckee barberry.  Four Seasons 4(4):2-18.
Whittemore, A. 1997. Berberis. Pp. 276-286 in Flora of North America Editorial Committee (eds.), Flora of North America North of Mexico, Vol. 3. New York and Oxford.
Williams, M. 1993. Berberis. Pp. 362-364 in Hickman, J.C. (ed.), The Jepson Manual: Higher Plants of California. University of California Press, Berkeley.
Williams, M. 2012. Berberis. Pp. 446-447 in Baldwin et al. (eds.), The Jepson Manual: Higher Plants of California. University of California Press, Berkeley.
Yu, C. C., & Chung, K. F. (2017). Why Mahonia? Molecular recircumscription of Berberis sl, with the description of two new genera, Alloberberis and Moranothamnus. Taxon, 66(6), 1371-1392.

Saturday, June 24, 2017

A new metric of floristic botany

Astronomers are not want to utilize relative measures: astronomical units, a measure of apparent brightness magnitude adjusted for distance, serves as an example. If cosmology can advance with such relative units, why not floristic botany? 

Introducing the Steyermark

Julian Steyermark (1909-1988) collected over 130,000 numbers of vascular plant specimens, as noted in the Guiness Book of World Records His maximal collection number I found is 132,006 (ref 1).  I therefore propose a unit of floristic botany, the Steyermark (StyM), set equal to 132,006 gatherings.

Floristic exploration depends on field work.  Voucher specimens are requisite for field work, hence for floristic documentation.  Gathering, processing, data entry, labeling and mounting of specimens is work, tedious work.  Once prepared, a specimen nowadays needs to be imaged before it is filed.   Any given botanist, however equipped and dedicated, contributes a finite number of specimens.   Their, and thus my magnitude, are finite.

Two California botanists of note of note are mentioned here: Robert Folger Thorne (1920-2015) collected ca. 63,000 numbers (G. Wallace, pers. comm.).  John Thomas Howell (1903-1994) gathered ca. 55,000 numbers.  

Accordingly:  Thorne =0.477 StyM, while Howell=0.407 StyM.  Many active California botanists have reached the 0.10 to 0.12 StyM range.  This author is 0.16 StyM, but not likely to graduate beyond 0.2!  

We can also set a relative measure of floristic inventory: specimens per unit area (ref 2).  For the western U.S.A., let us here take this to be 90% percentile of collection density as determined on a county basis: 5.55 specimens/square kilometer.  Given this, only 3,797,482 additional herbarium specimens are needed - ~28 StyM.   Presently, the western U.S.A. is at a density equal to much less.

Hay bailing has its value.

1     1.) Ann. Missouri Bot. Garden 76: 652-790. 1989.   Phytoneuron 2014-53: ISSN 2153 733X

Tuesday, June 20, 2017

Ackerson Meadow acquisition adds only 4 vascular plants to the Yosemite National Park Flora?

In 2015, Yosemite National Park moved to acquire 415 acres at Ackerson Meadow, adjacent to the western Park boundary in Tuolumne County (in the vicinity of Mather and the road to Hetch Hetchy). This acquisition was facilitated by a donation of the owners to the Trust for Public Land, and then by conveyance to the National Park Service.

Ackerson Meadow is a rare feature in the Sierra Nevada: a mid elevation (~4000 feet) non-forested setting supporting wet to dry meadows.   Ordinarily, such an addition to the Park ought to add considerably to the documented Yosemite National Park flora, being that the western Park boundary generally excludes much low to mid-elevation settings of the western slope of the Sierra. 

The region of Ackerson Meadow was part of Yosemite National Park in 1890 (act of Congress, October 1st 1890).  It was then removed, and any Public land in the vicinity was conveyed to the Forest Service by Congress acting on June 11, 1906.  By the time that John Muir has successfully argued for an expanded Yosemite in 1890, the land in the vicinity of Ackerson Meadow had been granted to James F. Ackerson in 1882 and 1884.  Portions of the Ackerson Meadow system are now managed by two agencies and under two administrative directives: about 200 acres of the meadow system remains within the Stanislaus National Forest.

Generally, the flora of the Yosemite region is well documented (Taylor 2010, Baldwin et al. 2017).  The four counties flanking Yosemite are rank about the 90th percentile for the western U.S. (Taylor 2014).  In 2014, Yosemite National Park raked in the 97th percentile for specimen density.  My analysis, based on records of herbarium specimens in the Consortium of California Herbaria, the acquisition adds only 4 potential new vascular plant records for the Park.

Species Added to YNP

Eryngium vaseyi var. vallicola (Apiaceae, JEPS101766) – this vernal pool coyote thistle is perhaps a new species: Preston et al (2012) stated :”plants keying here from cSNH (Tuolumne Co.) may be an undescribed taxon.”  Obviously, this possibility alone is worthy of funding for additional study.

Erythranthe utahensis (Phrymaceae) – a single collection is attributed to Ackerson Meadow (R. K. Vickery 191, August 26, 1949. UT).  The record was accepted by Nesom (2012), with the provision “have the taller habit of E. utahensis but with fewer flowers as in E. corallina and an apparently intermediate vesture”.  Obviously, this possibility alone is worthy of funding for additional study: E. utahensis is a CNPS rare plant, List 2B.1

Polygonum polygaloides ssp. confertiflorum (Polygonaceae, JEPS96724) – an annual of open dry sites that are wet to saturated in spring.  This location is the southerly reported station for this taxon.

Hosackia pinnata (Fabaceae, JEPS100871) – This wetland perennial also reaches its southerly geographic distribution in the Yosemite region.  The more common sister species in Yosemite, Hosackia oblongifolia var. oblongifolia, has been collected ~50 times in the Park.
The purpose of this post is to emphasize that a detailed floristic inventory of the acquisition, using rigorous methodology (Groom & Whild 2017), is needed.  The Yosemite Conservancy has undertaken an initial inventory of Ackerson Meadow: extensive, vouchered floristic inventory over a period of several years will be required to ascertain the exact value of this addition to Yosemite NP.  

Groom, Q. J. and S.J. Whild.  2017.  Characterization of false-positive observations in botanical surveys.  PeerJ 5:e3324; DOI 10.7717/peerj.3324

Nesom, G. 2012.  Taxonomy of Erythranthe sect. Simiola (Phrymaceae) in the USA and Mexico. Phytoneuron 40: 1–123.  Published 16 May 2012. ISSN 2153 733X Corrections to Map 9 and Map 15, 21 May 2012

Taylor, D.W. 2014.  Large inequalities in herbarium specimen density in the western United States. Phytoneuron 2014-53: 1–8.  Published 2 June 2014. ISSN 2153 733X

Taylor, D. W. 2010.  Flora of the Yosemite Sierra.  Lulu Press, Raleigh, NC. 382 pp.  ISBN 780557500529

Baldwin, B.G. et al.   2017. Species richness and endemism in the native flora of California.  Amer. J. Bot. 104 (3): 487 – 501, 2017  doi:10.3732/ajb.1600326

Tuesday, January 17, 2017

Minority opinion on classification of Ponderosa Pine

The recent study of Willyard et al (2017) on lineages of Ponderosa Pine (Pinus ponderosa) is important and at the same time highly problematic.  The study strongly demonstrates that Pinus ponderosa is a complex lineage containing several distinct taxa which merit taxonomic treatment. 
Willyard et al (2017) suggest treatment of the taxa in the lineage as full species:  Pinus ponderosa, P. benthamiana, P. scophulorum and P. brachyptera.   

This will not find wide acceptance in the non-botanical world of commerce.  A long history of practical use, common understanding, and governmental inertia will result in default back to a broadly circumscribed, single species model.  Unfortunately, the single taxon model fails to account for geographic and evolutionary distinct units within this clade, and is not a scientifically supported, proper classification.  Put crudely, the guy at the lumber yard is not going to care...!

The principal purpose of any classification is utility.  Treatment of the taxa of the Pinus ponderosa lineage as subspecies would have a much higher probability of gaining wide application.   Without reference to geography, the identification of individual trees is not easy, even with mature cones and bud-color features at hand, because the overall morphogical similarity between the individual taxa is substantial (Callaham 2013).  Users of a classification which employs infrataxa can refer only to Pinus ponderosa generally in instances where their determination of subspecies is unimportant (i.e. this timber is ponderosa pine) or in geographic areas where the taxa overlap (i.e. in the KR-CaRH region of California, where both P. ponderosa and P. benthamiana haplotypes are present). 

The five validly published taxa treated as subspecies are:
Pinus ponderosa P. Lawson & C. Lawson ssp. ponderosa, Agric. Man. 354 (-355). 1836
P. ponderosa ssp. ssp. benthamiana (Hartw.) Silba -- J. Int. Conifer Preserv. Soc. 16(1): 30. 2009
P. ponderosa ssp. brachyptera (Engelm.) Silba -- J. Int. Conifer Preserv. Soc. 18(1): 16. 2011
P. ponderosa ssp. scopulorum (Engelm.) A. E. Murray -- Kalmia 12: 23. 1982
P. ponderosa ssp. washoensis (H. Mason & Stockw.) A. E. Murray, Kalmia 12: 23. 1982.

The treatment of the taxa of Pinus ponderosa as subspecies is consistent with broad practice for many higher plants.  Treatment of the clade as varieties (where not all of the required names are valid) is not consistent with treatment models which have survived the test of time (Simpson 1945, Clausen 1951 Dobzhansky 1951, Stebbins 1966, Mayr 1982) and is inconsistent with common practice in the larger portions as applied to higher plants (Briggs & Walters 1971) worldwide.

In plant taxonomy, my opinion is that we devalue the worth of our effort when we do not defer to the practical needs of society at large whom consume our names.  

The five ponderosa pines are subspecies.

Briggs, D., & S. M. Walters.  1971    Plant Variation and Evolution.   White & Gilbert, U.K.
Callaham , R. Z. 2013 . Pinus ponderosa : Geographic races and subspecies based on morphological variation. USDA Forest Service, Pacific Southwest Research Station PSW-RP-265. Washington, D.C.
Clausen J.  1961.  Stages in the evolution of plant species.  Cornell Univ. Press, Ithaca, N.Y.
Dobzhansky, T.  1951.  Genetics and the origin of species.  Columbia Univ. Press, New York, N.Y.
Mayr, E.  1982.  Growth of Biological Thought: Diversity, Evolution, and Inheritance. Harvard Univ. Press Cambridge, M.A.
Simpson, G. G. 1945. The Principles of Classification and a Classification of Mammals. Bull. American Museum Nat. Hist. 85: 1-23.
Stebbins, G. L. 1966.  Processes of organic evolution.  Prentice Hall, Engelwood Cliffs, N.J.
Willyard, A. W. et al. 2017.  Pinus ponderosa: A checkered past obscured four species.  Amer. J. Bot. 104(1):1-21.