- 1862 P. Lawsonii Roezl ex Gordon, Pinet. Suppl. 64.
- 1905 P. Altamirani Shaw in Sargent, Trees & Shrubs, i. 209, t. 99.
Spring-shoots conspicuously pruinose, uninodal or not infrequently multinodal. Leaves in fascicles of 3, 4 or 5, not exceeding 24 cm. in length; resin-ducts internal, often with one or two medial ducts, hypoderm biform, endoderm usually with thin outer walls. Conelets mucronate. Cones from 5 to 7 cm. long on pliant peduncles, ovate or ovate-conic, oblique or sometimes symmetrical, deciduous, or persistent with a weak hold on the branch; apophyses nut-brown, flat or tumid, often protuberant on the posterior face of the cone, the umbo usually large and salient, forming a rounded button-like projection, on which the mucro is wanting.
A subtropical species of central and western Mexico, growing alone or associated with P. oocarpa, P. Pringlei and the subtropical forms of P. Montezumae and P. pseudostrobus. It is recognized among its associate species by its conspicuously glaucous foliage. The cone is very variable on trees of the same grove, both in size and in the protuberance of its apophyses. Gordon's specimen in the Kew herbarium consists of a single detached cone and a few leaves. The leaves differ from all that I have examined in showing thick-walled endoderm cells, but the cone corresponds with many of my own collection.
Fig. 239, Three cones. Fig. 240, Leaf-fascicle and magnified leaf-section. Fig. 241, Magnified cells of the leaf-endoderm.
