Pinus quadrifolia

Lanner (1974) believed P. quadrifolia to be a natural hybrid resulting from crosses between P. juarezensis and P. californiarum (called P. monophylla at that time, until P. californiarum was described as a species distinct from P. monophylla in 1987). Perry (1991) recognized P. quadrifolia and P. juarezensis as separate species, noting that "there are divergent opinions among botanists and taxonomists regarding [Lanner's] conclusions. Pending further studies of these taxa, I prefer to recognize P. quadrifolia as a separate species." Flora of North America Editorial Committee (1993) and Kartesz (1994 and 1999) accepted the name P. quadrifolia for the species, citing P. juarezensis as a synonym. Thus, there is one species (called by either name), which occasionally hybridizes with P. californiarum; the nomenclatural question hinges on whether the type of P. quadrifolia is from the species or from the interspecific hybrid. The extent to which this (broad-sense) P. quadrifolia taxon may continue to form hybrids with P. californiarum in the field is a matter of some question, at least in southern California (L. Merrill, pers. comm. 2009).

Rather limited distribution in southern California and northern Baja California, but not considered rare. Principal range in Sierra de Juárez and Sierra de San Pedro Mártir in Baja California Norte. Found in semi-arid to arid foothils and mesas at altitudes of 1,100-2,000 m.

Observational data suggests that this species may not be as susceptible as P. californiarum to infestation by the bark beetle Ips confusus following drought, at least in the Santa Rosa Mountains of southern California. Further research would help to confirm and explore this potential pattern (L. Merrill pers. comm. 2009).