Distribution of ‘long’ peduncles (red dots) in Texas E. sericeus

Click here for gallery of peduncle images for testing identification E. sericeus, E. alsinoides, E. rotundifolius. To check an ID in the gallery, just move the cursor onto the large image and the determination made by Bob Harms will appear on the image (in a small box), including the most recent different determination made by others (should these not agree). A general location for the specimen will also be given.

‘Long’ Peduncle Types in Evolvulus

In his A Monograph of the Genus Evolvulus (1934) van Ooststroom recognizes a distinct long-peduncled forma pedunculatus of E.sericeus (p. 130):
Habit of the typical E. sericeus Sw.; peduncle developed, short, 3–5 mm or much longer, attaining a length of 25 mm. Corolla up to 15 mm in diam.
Distribution: Texas, Northern Mexico.

E. sericeus 22 mm peduncle, Real Co., Texas

L. H. Shinners treatment in Correll & Johnston 1970 (p. 1244) categorizes forma pedunculatus v. Ooststr. as "rare." In fact it is the most common form along the SE edge of the Edward's Plateau, from Travis County to Val Verde County. (Note the red dots on the above map.)

E. alsinoides regularly has longer peduncles, and occasionally regional keys use this feature to distinguish it from E. sericeus; e.g., Henrickson & Johnston 1997, A flora of the Chihuahuan Desert Region, unpub.:

A. Fls. borne on distinct, slender, filiform peduncles 1-2(-4) cm long; … lvs. never glabrous above.
… 1. E. alsinoides
AA. Fls. sessile or short pedicillate in the lf. axils, (very rarely long pedunculate as in E. alsinoides,
but if so with the upper lf. surface glabrous); … lvs. sericeous or glabrous above.
… E. nuttallianus, E. sericeus

E. alsinoides 15 mm peduncle, Presidio Co., Texas

Not surprisingly a number of E. sericeus forma pedunculatus specimens have been identified as E. alsinoides, since their distribution overlaps (or nearly so). [The above Henrickson & Johnston key suffices to correct these, since these forms are not sympatric with those with a pubescent upper leaf surface.]

Also with somewhat longer peduncles are specimens of E. rotundifolius from the state of Durango in Mexico.


E. rotundifolius 3.5 mm peduncle, Durango, Mexico

Of course, long & longer are relative concepts, and D. Austin (in regional New Mexico (1990) & Arizona (1998) treatments, valid for those areas, but not Texas) appropriately relates the peduncle length to the subtending leaf length:

Peduncles filiform, longer or shorter than the subtending leaves.
… E. alsinoides, … E. arizonicus
Peduncles absent or very short and stout, always shorter than subtending leaves.
… E. nuttallianus, … E. sericeus

Plant Resources Center Home Page — Flora of Texas — Evolvulus