A key to Thelypodium in New Mexico that I wrote a year ago, after finding existing keys for the genus in our area somewhat unsatisfying:
1 Stem leaves sessile, entire or rarely denticulate; pedicels stout, ca. 0.5 mm wide – Thelypodium integrifolium subsp. gracilipes
1 Stem leaves petiolate, at least the lower pinnately lobed; pedicels slender, ca. 0.25 mm wide (or stout in T. texanum)
2 Sepals ascending at anthesis, bases of petals and stamens not directly visible; stamens erect, tetradynamous (the outer two conspicuously shorter than the other four); replum constricted between the seeds — Thelypodium laxiflorum
2 Sepals and stamens spreading at anthesis, bases of petals and stamens directly visible; stamens ascending, equal in length; replum not constricted between the seeds
3 Uppermost stem leaves pinnately lobed; mature fruits stiffly horizontal to ascending, usually 1.3 mm wide or more – Thelypodium texanum
3 Uppermost stem leaves entire or toothed, rarely with a couple of lobes near the base; mature fruits horizontal to reflexed, often drooping, usually 1.2 mm wide or less – Thelypodium wrightii
Some brief notes:
Thelypodium integrifolium subsp. gracilipes is basically a species of relatively moist, salty places (playas, alkaline flats, salty springs or washes, etc.) and is definitely present in the northwest corner of the state (San Juan County, probably Rio Arriba and McKinley counties as well) but has been reported from a number of other areas. Probably most of these are misidentifications, but I have not seen the specimens.
We have only one record of Thelypodium laxiflorum in the state, in San Juan County. Thelypodium integrifolium also has ascending sepals and fairly “closed” flowers; this feature is quite obvious on live plants but can be obscured in pressed specimens.
Thelypodium texanum has generally been known under the name Sibara grisea in New Mexico. It is found on and near limestone cliffs in southeastern New Mexico (Eddy and Otero counties).
Thelypodium wrightii occurs in a range of habitats, but I have seen it mostly in moist canyons at intermediate elevations (ca. 6000-7000 feet). This is the most abundant Thelypodium in the state by a wide margin. Consequently, misidentifications of Thelypodium in the state consist mostly of calling Thelypodium wrightii something else. This is the same kind of mistake that is common with Erysimum. I think this is a general rule: If one species in a genus is dramatically more abundant than the others, variation within that species is likely to be misinterpreted as representing the other, relatively rare, species. I think this results from an overestimation of one’s thoroughness in sampling. Surely, after seeing several hundred Thelypodium in New Mexico, you must have seen all four species in the state! Therefore, any variation you can observe must be the same variation discussed in taxonomic works on the genus. Of course, if one species is far more abundant than the others… you might have only seen that species. You might then spend hours trying to figure out how the variation within that one species can be forced to correspond with the published taxonomic work on the genus, which says there are four species in your area. And thus you are led astray. This, by the way, is why access to a comprehensive herbarium is often a necessity. Many errors can be avoided if you have specimens of the relevant species available to compare side-by-side. That said, misidentifications in Thelypodium are understandable with fragmentary specimens. For instance, the leaves of Thelypodium wrightii are progressively reduced as you move up the stem, becoming entire and nearly sessile near the bases of the inflorescences. If only the upper parts of the stems are collected (which is common, because Thelypodium wrightii can be 5-6 feet tall and will not easily fit on an herbarium sheet), this can easily lead to a misidentification of the specimen as Thelypodium integrifolium. The lower petiolate, pinnately lobed leaves can also senesce later in the season, causing the same confusion even if you have the whole plant in hand. In such cases, the narrow pedicels and widely spreading sepals of Thelypodium wrightii (vs. stout pedicels and ascending to erect sepals in Thelypodium integrifolium) should allow correct identification. Or, if in doubt, calling everything in the genus “Thelypodium wrightii” will result in the correct identification 90+% of the time!