Pines

One of the most familiar feature of pines is their cones. Biologically, a pine cone is simply a fertilized female strobilus containing seeds within.

While their economic significance is not as great as that of pines, which are harvested for timber (see above), the pinyon pines (Pinus cembroides, P. monophylla, P. quadrifolia, and P. edulis ) are prolific producers of edible pine "nuts," which are technically seeds. These seeds are often used in salads, sauces, desserts, and other foods. The pinyon pines are native to semi-arid regions of the western United States and Mexico.

The largest pine cones come from the sugar pine (Pinus lambertiana). This species grows in western North America and its pine cones are typically 15-18 in (38-46 cm) long and 4 in (10 cm) wide. The cones of the big cone pine (Pinus coulteri), a native of California, are somewhat smaller, but can weigh over 4.4 lb (2 kg), heavier than any other species.

A Scotch pine. Photograph by James Sikkema. Reproduced by permission.

One of the most interesting pine cone adaptations occurs in jack pine (Pinus banksiana), pitch pine (P. rigida), knobcone pine (P. attenuata), and several other species. The cones of these species are serotinous, meaning that they are "late opening." In particular, the pine cones remain closed long after the seeds have matured. They typically open up to disperse the seeds only after exposure to very high temperatures, such as occurs during a fire. At the biochemical level, the heat of a fire apparently softens the resins that hold together the scales of the cone. Pine trees with serotinous cones often grow in ecosystems that have a high frequency of fires. For example, the pitch pine grows in the New Jersey pine barrens, where natural or man-made fires have occurred for many centuries.