Pinus is also peculiar in the dimorphism of shoots and leaves and in their constant interrelations with the diclinous flowers. Evolutionary processes develop features peculiar to Pinus alone (the oblique cone, etc.), but confined to a limited number of species.
SECTIONAL CHARACTERS
There are several characters that actually or potentially divide the genus into two distinct sections, popularly known as Soft and Hard Pines.
- 1. The fibro-vascular bundle of the leaf, single or double.
- 2. The base of the bract subtending the leaf-fascicle, non-decurrent or decurrent
- 3. The phyllotaxis of the cone, simple or complex.
- 4. The flower-bud, its less or greater development.
Some characters indicate the same distinction but are subject each to a few exceptions.
- 5. The fascicle-sheath, deciduous or persistent.
- 6. The walls of the ray-tracheids, smooth or dentate.
- 7. The connective of the pollen-sacs, large or small.
- 8. The formation of bark, late or early.
SUBSECTIONAL CHARACTERS
An exact subdivision of the Soft Pines is possible on the following characters.
- The umbo of the cone-scales, terminal or dorsal.
- The scales of the conelet, mutic or armed.
- The pits of the ray-cells, large or small.