Abstract Detail

Systematics

Campbell, Julian [1].

Green/red and white ashes (Fraxinus section Melioides) of east-central North America: taxonomic concepts and polyploidy.

Taxonomic problems among the green/red and white ashes (Fraxinus section Melioides) of east-central North America are reviewed. Within green/red ashes (F. pennsylvanica sensu lato), a distinction is made between largely southern/eastern plants (referable to var. subintegerrima and var. pennsylvanica*) and largely northern/western plants (referable to var. campestris and var. austinii*). The latter include the common cultivar “Marshall’s Seedless”. They tend to have smaller leaves, shorter petiolules, more leaflet serration, larger buds relative to leaf scars, and smaller samaras. Within both groups, relatively pubescent variants (*) tend to have larger samaras, and may also be usefully segregated. Pumpkin ash (F. profunda) is generally assumed to be a distinct hexaploid species, but there is only one reported chromosome count, and even with fruits there is uncertainty in distinguishing some collections from F. pennsylvanica. White ashes have been interpreted as a polyploid series (americana = 2x, smallii = 4x, biltmoreana = 6x), based largely on cytological studies during 1947-83, but there have been few reliable chromosome-counts in polyploids and these lack supporting collections. Recent results from flow cytometry indicate only hexaploids among plants referable to F. smallii from Kentucky. Relatively reliable reports of tetraploids are more restricted to southern regions than suggested by Guy Nesom in 2010. The only obvious difference between smallii and biltmoreana is that the latter is more densely pubescent, especially on rachises and young twigs. It is suggested that most plants referable to F. smallii should be treated as a variety of F. biltmoreana. Diploid F. americana (sensu stricto) remains quite variable in pubescence and in samara size, which displays a bimodal tendency, but there is no obvious basis yet for further division of this species into varieties. This taxonomic scheme is supported by keys, state-distribution maps, principal components analysis of morphometric data from 160 collections, and frequency distributions of samara sizes.

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Keywords:
Fraxinus
taxonomy
Polyploidy.

Presentation Type: Oral Paper
Session: 41, Systematics III: Euasterids
Location: Sundance 4/Omni Hotel
Date: Wednesday, June 28th, 2017
Time: 3:45 PM
Number: 41008
Abstract ID:108
Candidate for Awards:None