Members of the Euphorbia fendleri complex endemic to Mexico
The Euphorbia fendleri complex (as I'm defining it here) includes E. fendleri and many additional species that are somewhat weakly differentiated from it. In the US, this includes E. fendleri, E. chaetocalyx, and E. triligulata. In Mexico, all three species above are included in addition to three endemics, E. fruticulosa, E. scopulorum, and E. crepitata (non-Mexico endemics include E. fendleri, E. chaetocalyx, and E. triligulata). Each of the endemics of Mexico have multiple varieties defined below. The best treatment was provided by M.C. Johnston in the 70s (key starts here). Below are some notes and photos of the species of interest.
I'm currently studying these species, so if you happen to see them, please let me know!
E. fruticulosa
Defined mostly by it's lack of appendages, woody stems, and lack of hairs (except for the rare var. hirtella). Stems not sticky to my knowledge.
E. fruticulosa var. fruticulosa (left)
Relatively widespread in limestone and gypsum. Central Coahuila and W Nuevo León
E. fruticulosa var. hirtella (right)
Super rare. Only known from 2 occurrences. Occurs in gypsum around the mountains NE of Torreón (e.g., San Lorenzo).
https://was.tacc.utexas.edu/fileget?coll=TEX-LL&type=O&filename=sp61440512961439729340.att.jpg
E. scopulorum
Plant hairy except for var. nuda. Appendages deeply parted (essentially identical to E. triligulata) except for var. inornata where they are absent.
Picture of E. triligulata cyathium (no close-ups of E. scopulorum except for var. inornata exist):
E. scopulorum var. scopulorum (left)
Widespread in central Coahuila. Appears to prefer limestone, but I'm not certain on this.
E. scopulorum var. inornata (right)
Mostly W Nuevo León and E Coahuila. Appears to prefer limestone, but I'm not certain on this.
E. scopulorum var. nuda
Super rare. Only 2 known occurrence records. Appears restricted to the Mountains NW of Saltillo. This plant looks nearly identical to E. triligulata if it had broader leaves. One of the hypotheses in my research is that they are the same species.
E. crepitata
Defined by its ridged seeds. In the field, defined by its sticky stems. Both varieties appear to be gypsum endemics and are most commonly collected around Cuatrociénegas. I haven't fully figured out how to distinguish this from E. fruticulosa from photos. I'm hoping that going into the field and seeing them together will resolve this.
E. crepitata var. crepitata (right)
E. crepitata var. longa (left)
https://sweetgum.nybg.org/images3/3723/836/04020633.jpg
https://was.tacc.utexas.edu/fileget?coll=TEX-LL&type=O&filename=sp64663013086051446914.att.jpg
