Purhepecha oak (Quercus purhepecha), new species of shrub oak endemic to the state of Michoacán, Mexico

NEWS - In Mexico, several Quercus shrubby species are taxonomically very problematic including 8 taxa with similar characteristics. Now researchers report the purhepecha oak (Quercus purhepecha De Luna-Bonilla, S. Valencia & Coombes sp. nov.) as a new tomentose shrubby white oak species with a distribution only in the Cuitzeo basin in the Trans-Mexican Volcanic Belt (TMVB).

Quercus Linnaeus (1753) subdivided into 2 subgenera and 8 sections of which section Quercus (white oaks) has the widest distribution in the Americas, Asia and Europe. This section is very diverse in Mexico and Central America with phylogenomic evidence indicating recent and accelerated speciation in these regions.

The number of shrubby oak species in Mexico is still uncertain. De Luna-Bonilla of the Universidad Nacional Autónoma de México and colleagues found at least 3 taxa in the TMVB, specifically Quercus frutex Trelease (1924), Quercus microphylla Née (1801) and Quercus repanda Bonpland (1809).

In 2016, Allen J. Coombes of Benemérita Universidad Autónoma de Puebla and Susana Valencia-A of the Universidad Nacional Autónoma de México recognized a specimen that was distinct from all other species, lacking seeds and insufficient to base a description on.

Q. purhepecha is a rhizomatous shrub, 0.3–0.7 m tall, twigs (1)1.3–2.3(2.7) mm in diameter, gray to pale-reddish, slightly furrowed, glabrous to tomentose, retaining sparse stipitate fasciculate trichomes, with conspicuous lenticels; buds ovoid, 2.6–3 mm long, scales broadly ovate, glabrous, reddish-brown, margin irregularly fimbriated.

Mature leaves with petioles 2.3–3.4 mm long × 1.0–1.3 mm in diameter, yellowish to slightly reddish toward the base, glabrescent with sparse whitish fasciculate stipitate trichomes, stipules linear to narrowly lanceolate 2.8–5.6 mm long, glabrescent or sparsely floccose, retaining grayish sessile fasciculate trichomes, usually persistent even when leaves are mature.

Lamina coriaceous, slightly obovate, oblong, ovate-lanceolate, rarely ovate, 3.5–5.2(7) cm long × (1.2)1.4–2(2.5) cm wide, 2.5–3 times longer than wide, apex acute, attenuate to rounded, margin thickened, flat or slightly revolute, entire or with 1–2 short mucronate teeth, some leaves of juvenile shoots from the base of the plant or the rhizome may have up to 7 teeth almost from the base, base rounded or slightly subcordate.

Secondary veins (6)7–10(12) on each side of the midvein, ascending, moderately curved towards the margin, branched and anastomosed before reaching the margin, adaxial blade surface dull, glaucous, secondary veins slightly impressed, glabrous to glabrescent.

Preserving scarce fasciculate trichomes laxly distributed towards the base of the lamina and midvein, abaxial blade surface whitish to grayish, tomentose to glabrescent, with fasciculate shortly stipitate trichomes with whitish crispy rays becoming dark with age, laxly distributed, not obscuring the white-papillose and somewhat bullate epidermis.

Fruits annual, 1–2 on a grayish, pubescent to glabrous peduncle 0.7–2 cm long × 1.2–2.5 mm in diameter; cupules hemispheric to slightly conical, 8.3–12 mm long × 13–19 mm in diameter, scales triangular to narrow-triangular towards the margin of the cupule, base of scales keeled and white-pubescent, nuts brownish, glabrous, ovoid to oblong-ovoid, 15.5–18.3 mm long × 11–15 mm in diameter, ca. ½ their total length included in the cupule.

Q. purhepecha is similar to Q. laeta, Q. frutex, Q. microphylla and Q. repanda. It can be distinguished from Q. laeta by its shrub form, rhizome, and toothed and non-toothed leaves. From Q. frutex it can be distinguished by the shape of the rhizome and the leaves that are not or only slightly whorled.

From Q. microphylla it can be distinguished by the shape of the rhizome and the presence of short fascicular trichomes, stipes vs. short-stalked on the abaxial surface of the blades. From Q. repanda it can be distinguished by the leaves that are not or only only slightly whorled (clearly whorled in Q. repanda) and the absence of yellow trichomes.

The new species grows in Michoacán, Mexico, at an elevation of 2100-2450 m, on the edge of oak forests, in patches that spread mainly by rhizomatous, on poor and shallow soils. Associated with Q. castanea Née (1801), Q. deserticola Trelease (1923) and Erythrina leptorhiza Mociño & Sessé ex de Candolle (1825).

Flowering in January and February, fruits ripen in September. Some trees have numerous galls. It is caused by wasps of the genus Atrusca Kinsey (1936). The initial conservation status is Critically Endangered (CR). This specific epithet is given to the indigenous P’urhepechas people who inhabit Michoacán, where the species is endemic.

The species reproduces vegetatively, making it very difficult to determine the exact number of individuals, but it can be concluded from fieldwork that the number is low. In addition, the distribution near the city of Morelia, which is experiencing rapid growth, means that conservation plans for the species should be considered a priority.

Original research

Oscar Angel De Luna-Bonilla, Antonio González-Rodríguez, Hernando Rodríguez-Correa, Javier Piña-Torres, Allen J. Coombes & Susana Valencia-A (2024). Quercuspurhepecha (Fagaceae), a new species of shrub oak endemic to the state of Michoacán, Mexico. Phytotaxa 670 (4): 191–202, DOI:10.11646/phytotaxa.670.4.1

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