| Bases of the fascicle-bracts non-decurrent | A—HAPLOXYLON |
| Umbo of the cone-scale terminal | a—Cembra |
| Seeds wingless. | |
| Cones indehiscent | I. Cembrae |
| Cones dehiscent | II. Flexiles |
| Seed with an adnate wing | III. Strobi |
| Umbo of the cone-scale dorsal | b—Paracembra |
| Seeds wingless | IV. Cembroides |
| Seed-wing short, ineffective | V. Gerardianae |
| Seed-wing long, effective | VI. Balfourianae |
| Bases of the fascicle-bracts decurrent | B—DIPLOXYLON |
| Fascicle-sheath or seed of Haploxylon | c—Parapinaster |
| Fascicle-sheath deciduous | VII. Leiophyllae |
| Fascicle-sheath persistent. | |
| Seed-wing of the Strobi | VIII. Longifoliae |
| Seed-wing of the Gerardianae | IX. Pineae |
| Fascicle-sheath persistent, seed-wing articulate, effective | d—Pinaster |
| Base of wing-blade thin or slightly thickened. | |
| Cones dehiscent at maturity. | |
| Pits of ray-cells large | X. Lariciones |
| Pits of ray-cells small | XI. Australes |
| Cones serotinous, pits of ray-cells small | XII. Insignes |
| Base of wing-blade very thick | XIII. Macrocarpae |
HAPLOXYLON
Bases of the bracts subtending leaf-fascicles not decurrent. Staminate flowers not sufficiently developed in the bud to be apparent. Spring-shoots uninodal. Fibro-vascular bundle of the leaf single. Cone symmetrical, of relatively fewer larger scales, its tissues softer. Bark-formation late, the trunks of young trees smooth. Wood soft and with little resin, of uniform color and with relatively obscure definition of the annual rings. Tracheids of the medullary rays with smooth walls.
All the species of this section, except P. Nelsonii, have deciduous fascicle-sheaths. There are but two species of Diploxylon with deciduous sheaths, P. leiophylla and P. Lumholtzii, both of them easily recognized. The deciduous sheath, therefore, is an obvious and useful means for recognizing the Soft Pines. On the characters of the fruit and the wood Haploxylon can be divided into two subsections.
| a. Cembra | Umbo of the cone-scale terminal. |
| b. Paracembra | Umbo of the cone-scale dorsal. |
Cembra
Umbo of the cone-scale terminal. Scales of the conelet unarmed. Leaves in fascicles of 5, the sheath deciduous, the two dermal tissues distinct, the hypoderm-cells uniform. Pits of the cells of the wood-rays large.
| Seeds wingless. | |
| Cones indehiscent | I. Cembrae. |
| Cones dehiscent | II. Flexiles. |
| Seeds with an adnate wing | III. Strobi. |