mexicana as the dominant element are considered a relict and paleoendemic
vegetation established in areas that presumably served as Pleistocene refuges of flora and fauna in Mexico (Rzedowski 1991).
is an ancient relict with no apparent closely related extant taxon (Table X; Keener, 1983).
This suggests that these two genera are paleoendemics.
Nevertheless, the blind species in the family linyphiid, Centromerus bulgarianus (Drensky 1931), Troglohyphantes drenskii Deltshev 1973 and Troglohyphates bureschianus Deltshev 1975, all species with primitive three branched paracymbia, also can be regarded as probable paleoendemics (Deltshev 1996).
This is probably the case in the more marginal of the section Polium species, such as those of subsection Rotundifolia (Sauvage & Vindt, 1955) or of subsection Simplicipiliosa (Puech, 1976), especially those, such as chasmophyte paleoendemics
(Puech, 1976; Crespo et al.
Species-based projects: These would identify species of special and immediate concern-- for example, paleoendemics and anthropogenic endemics that have restricted and shrinking distributions, respectively.
He shows that this region contains paleoendemics and neoendemics, illustrating both the antiquity of speciation processes and the continuing relevance of spatial heterogeneity to biological diversity.