Pinus Johannis - History

History

Pinus johannis is a recently described pinyon pine, discovered by Elbert L. Little in 1968 when comparing pinyons growing in Arizona with those of typical Mexican pinyon (Pinus cembroides) in Mexico; he described it as a variety of Mexican pinyon, Pinus cembroides var. bicolor, noting the very different stomatal placing on the leaves; it also differs in needle number, with 3–4 per fascicle, rather than 2–3; in the cones having thinner scales; and in having a denser, more rounded crown. Further research by the French botanist Marie-Françoise Robert-Passini, the American botanists Dana K. Bailey and Frank G. Hawksworth and others, has shown that it is better treated as a distinct species. Although often occurring together with Mexican pinyon, it is reproductively isolated from that by its pollination being a month to two months later in summer, rather than in spring, thereby preventing hybridisation.

As Robert-Passini and Bailey & Hawksworth were working in different areas at about the same time, it was raised to species rank twice, first as Pinus johannis by Robert-Passini (naming it after her husband Jean) examining specimens in the Sierra Madre Oriental in Mexico, and then later as Pinus discolor by Bailey & Hawksworth examining specimens in the northern Sierra Madre Occidental in Arizona.

There are slight differences between the plants in the two ranges; those in the eastern being more shrubby and with larger cones than those in the western range, and also differences in the resin composition; they are though generally very similar and recognition of both as separate species from each other does not appear warranted.

Some botanists also still include P. johannis in Mexican pinyon as a variety or even not distinguished at all, accounting for reports of "Mexican Pinyon" in Arizona and New Mexico. This is despite the two frequently occurring together at the same sites with no hybridisation.

P. johannis is most closely allied to Orizaba pinyon (Pinus orizabensis) and Potosi pinyon (Pinus culminicola), with which it shares the leaf structure with the stomata confined to the inner faces; it differs from the former in the smaller cones and seeds, and from the latter in fewer needles per fascicle (3-4 vs 5).