Flower:

Flowers are borne in structures called cones (strobili) with separate male and female cones on the same tree. Male cones are cylindrical, 1/3 to 2/3 inch long, in dense clusters at the base of a candle (new branchlet), the growing bud tip just above. The female strobili form on the upper portion of the new candle, small and egg-shaped, about 3/8 inch long, pinkish colored on a scaly brown stalk.

Leaves and bark:

Leaves are needle-like, ¾ to 2 inches long, in bundles of two that spiral up around the branch, the pair ascending to widely spreading, and often twisted. Needles are rounded on the outside but facing surfaces flattened (D shaped in cross section), or channeled (U shaped in cross section).

Twigs are reddish brown and scaley. The bark becomes grayish brown and scaly on branches, old bark on trunk, brownish gray to nearly gray-black with vertical ridges, often flaky.

Buds are reddish brown with a whitish resinous coating, cylindrical, about ½ inch long with an abrupt, dull tip.

Fruit:

The fruit is a hard cone that takes two years to mature. The first year small and egg shaped, about ½ inch long with a short, thick stalk. Cones are 1 to 2 inches long when mature at the end of the second year, typically a blocky horn shape with the tip curled towards the branch, sealed closed by resin (serotinous) until released by heat of fire, though a few cones may open up without such heat.

Notes:

Jack Pine is Minnesota's smallest native pine and has the shortest needles of all Pinus species in Minnesota. While typically under 70 feet tall, it can attain a height of 100 feet on better soils where it is mixed in with other forest tree species. It is very tolerant of dry, sandy sites where it can form pure, often straggly, stands. A pioneer species, its heat dependent cones allow it to reproduce quickly following a fire, though on sites favorable to other species, it is ultimately replaced.