Philadelphus mearnsii W.H. Evans ex Rydb.

Family: Hydrangeaceae

Discussion: In 1999, Chris Frazier published "A Taxonomic Study of Philadelphus As It Occurs in New Mexico" in the New Mexico Botanist. The following is a synopsis of Frazier's paper and must serve as the review document for all the Philadelphus species on our review list. Frazier made a complete review of the literature concerning southwestern Philadelphus species. He also examined 98 UNM specimens and scored them for a 31 character data set which was used for a principal component and discriminant analysis.

Frazier found that many of the characteristics considered important by previous authors were unreliable. His analysis found three characters: axillary bud type (exserted vs. enclosed); leaf face (isofacial or bifacial); and sepal tomentosity (glabrous or ciliate vs. tomentose) all perfectly correlated and with factor loadings above 0.9 on the first axis. Two clusters are obvious which he calls the "microphyllus group" (buds enclosed, leaves bifacial, sepals persistent) and "mearnsii group" (buds exposed, leaves isofacial, sepals deciduous in fruit).

When other characters are applied, the PCA of these groups show that P. hitchcockianus of the Guadalupe Mts. and P. mearnsii of southwest and south-central NM are fairly tightly clustered and not much different. The "microphyllus group" is much more spread out and separable into three slightly overlapping taxa. Frazier proposes only the four following taxa be recognized in NM:

Philadelphus mearnsii W.H. Evans ex Rydb. (syn = P. hitchcockianus Hu).
This is a low growing xeric shrub with a distinct maple syrup odor. The only difference Frazier could detect between the Guadalupe Mts. population and the other P. mearnsii collections was glabrous hypanthia in the Guadalupes vs. slightly strigose for the rest. Frazier believes this is too little to distinguish two taxa. Occasional in canyons and cliffs of Chihuahuan desert mountains. In New Mexico it ranges from Hidalgo County, as far north as the Fra Cistobal Mts. and east to the Guadalupe Mountains. Also occurs in northern Mexico and west Texas. Spellenberg (1981) cites 12 NM collections of P. mearnsii prior to Frazier's proposal to include P. hitchcockianus in that species. Spellenberg's report was sufficient to drop this species to a 3C rank in federal status.

Philadelphus microphyllus A. Gray subsp. microphyllus (syn = P. m. var. ovatus Hu).
Large bush with bifacial leaves and glabrous or nearly glabrous hypanthium and sepals. This is our most common Philadelphus. In NM it ranges from San Juan Co. south to Grant Co. then northeast to Colfax Co. North to Wyoming.

Philadelphus microphyllus subsp. argenteus(Rydb.) C.L. Hitchcock (syn = P. argenteus Rydb., P. madrensis Hemsl., P. occidentalis A. Nels. as applied by Martin & Hutchins)
Hypanthium strigose with straight hairs. This is the common Philadelphus of southern NM and adjacent southwest AZ and north-central Mexico.

Philadelphus microphyllus subsp. argyrocalyx (Woot.) C.L. Hitchcock (syn = P. argyrocalyx Woot., P. ellipticus Rydb., P. wootonii Hu
Hypanthium tomentose. This subspecies is endemic to Sacramento Range and Capitan Mountains of south-central NM - Lincoln and Otero Counties. (ed. note: It is fairly common within its limited range.) For P. wootonii Frazier says "Hu described P. wootonii as a sympatric congener of P. argyrocalyx distinguished from it by having disciform flowers, pubescent center on the disk and base of style, and short-tailed seeds. The corolla character is unreliable and the pubescence of the disk likely to be an inconsistent correlate with the overall greater density of pubescence of subsp. argyrocalyx. Seed tail length is a developmentally and environmentally variable character. I see no reason to distinguish P. wootonii from argyrocalyx." (ed. note: This critique is likely correct, but I must caution: P. wootonii is apparently only known from its type collection and Frazier has not seen the type specimen.)

Additional note: Frazier believes there is no documented proof that Philadelphus serpyllifolius occurs in NM. Hitchcock (1943) did cite one New Mexico locality for P. serpyllifolius in his 'Materials Seen' section, but this is for the type which was collected "between western Texas and El Paso, New Mexico" -- El Paso is in western Texas. Frazier also thinks the Hu map (1956) that places serpyllifolius in southwest NM and southeast AZ is somehow mixed up with the distribution of P. mearnsii. (ed. note: Even if P. serpyllifolius is in NM, it ranges from west Texas to Coahila, and would be a peripheral here.)

Important Literature:

Frazier, C.K. 1999. A taxonomic study of Philadelphus (Hydrangeaceae) as it occurs in New Mexico. The New Mexico Botanist 13:1-6.

Hitchcock, C.L. 1943. The xerophyllous species of Philadelphus in southwestern North America. Madrono 7:35-56.

Hu, S. 1956. A monograph of the genus Philadelphus. Jour. Arn. Arb. 37:15-90.

Spellenberg, R.W. 1981. Status Report on Philadelphus mearnsii. Submitted to USFWS, Albuquerque, NM.

Information Compiled By: Bob Sivinski, 1998
(last updated by J. Mygatt, May 2008)