This taxon belongs to Section Bartonia which contains the greatest diversity of Mentzelia species in New Mexico. The species of Section Bartonia are also the most confusing and appear to have few distinct boundaries between taxa. The most extreme forms have been named, but the intermediate forms are actually more common and very difficult to assign a name. Such is the case with Mentzelia perennis.

The type locality of M. perennis is Otero County, Round Mt. between Tularosa and Mescalero on gypseous soil. The type has yellow flowers, short capsules and long leaves with a few short lobes. Other yellow-flowered plants from Yeso Fma gypsum in this same vicinity along the Sacramento Escarpment have long, entire leaves (a few cauline leaves may be lobed). These are the characteristics that also describe Mentzelia saxicola which occurs on gypsum in the Texas counties of Presidio, Hudspeth, and El Paso. The form with entire leaves also reappears in a gypsophilic population near San Felipe, Sandoval County, New Mexico. Therefore, we must choose from either of two situations. The first and least likely is: we have numerous locations of M. saxicola in New Mexico and M. perennis is narrowly endemic to its type locality. The preferable second choice is M. saxicola is a synonym of M. perennis (perennis has priority), which extends the range of the latter well into Texas.

The most confusing intermediates appear to be between Mentzelia perennis and Mentzelia humilis which also occur on gypsum or limestone. Both have short, globular capsules and are strongly perennial with a woody branching caudex. The type of M. humilis has short pectinate-laciniate leaves and white flowers with narrow accuminate petals. In the strict sense, M. humilis occurs in NM only on limy and gypseous soils in southeastern part of the state. The variously lobed-leaf perennials with short capsules in the remainder of the state all have broader acute petals that dry yellow and appear to be grading into other species - probably the M. perennis form. Therefore, leaf length and lobing are not useful in distinguishing these taxa. Leaf and stem pubescence may be useful (but not entirely consistent) in separating M. perennis from M. humilis. The pubescence of the yellow-flowered, short capsule perennial is almost always retrorsely curved or appressed. I am calling these M. perennis. The pubescence of M. humilis in eastern NM is mostly antrorse (except in Guadalupe County). The intermediate forms are common on gypseous soils throughout central NM. They cannot be assigned a name unless we adopt a very broad circumscription of M. perennis which I define as follows:

Perennials with branching woody caudex; leaves entire to variously lobed; pubescence pustulate, retrorsely curved or appressed (rarely nearly glabrous); petals lanceolate-acute, drying yellow, capsules short globular or cup-shaped. Locally abundant on gypsum (rarely other limy soils) throughout central NM (Otero, Sandoval, Socorro, Torrance, Valencia Cos.) to west Texas (El Paso, Hudspeth, Presidio counties).