9sepalpics.jpg
E. nuttallianus, E. arenarius & E. sericeus/E. discolor sepals. Click for page with larger images with identification.

Evolvulus Sepals as Differentiae
by Bob Harms (email-here)

Sepal differences have played a significant role in distinguishing E. sericeus/E. discolor and E. nuttallianus1, from Nuttall's 1818 description to the present. Pursh in publishing the new E. argenteus, 1816, does not describe the sepals, apparently relying on vestiture differences to distinguish these two taxa ("foliis oblongis utrinque sericeo-tomentosis" - leaves sericeo-tomentose on both sides). Shinners 1970 likewise makes no mention of sepals (beyond "sepals 5" for the genus) — an unfortunate decision, since he relies upon leaf pubescence as a key feature, but this is valid only east of the Trans–Pecos.
1Earlier synonyms E. argenteus (Pursh), E. pilosus (Nuttall).

source E. nuttallianus E. sericeus
Current recognized authority
van Ooststroom 1934 lanceolate or narrow-lanceolate narrow-oblong-lanceolate to oblong-lanceolate
Early (19th century) investigators
Pursh 1816
Nuttall 1818 linear ovate, acuminate
Don 1831-38 partly linear, and acuminated lanceolate, acute, with recurved tops
de Candolle 1845 linari-lanceolatis 2 1/2 lin. longis acutis
    extus sericeis
Gray 1878 lanceolate-subulate ovate-lanceolate
Recent publications
Kearney & Peebles 1960 linear or narrowly lanceolate lanceolate or ovate lanceolate
Shinners 1970*
Martin & Hutchins 1981 linear to linear-lanceolate lanceolate to ovate-lanceolate
Austin 1998 lanceolate to narrow-lanceolate,
    4–5 mm long, spreading villous
oblong-lanceolate,
    3–5 mm long; appressed-pilose
Diggs 1999** lanceolate to narrowly lanceolate,
     4–5 mm long, spreading pilose
oblong lanceolate,
    3–5 mm long, appressed pilose
*In Correll & Johnston 1970.
**for N. Central Texas (obviously based on work by Austin)

An attempt to apply the features of more recent taxonomists in the above table to the nine images at the top of this page (or better, on the page with their larger images) will produce neither uniform results nor the desired results. In part, the terms seem to leave open potential overlap (i.e., determining the boundaries between linear-lanceolate, narrowly lanceolate, lanceolate, oblong-lanceolate, ovate-lanceolate). And in part because at the eastern edge of its range E. nuttallianus has rather broad sepals, close to ovate with an acuminate apex (e.g., in Fannin Co., Hays Co., Travis Co.). Yet a third consideration comes into play when vestiture–based determinations incorrectly classify plants of the Trans–Pecos and adjacent Mexico with broad–based sepals, i.e., E. discolor & E. arenarius, as E. nuttallianus.


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