It reaches a height of 30-35 m (100-115 ft) and a diameter of 0.7 m (28"). In the past, they reportedly grew to 47 m (154 ft) with a diameter of 1.2 m (47").
The bark is thick, reddish-brown, and scaly. The dark green, needle-like leaves occur in bundles of three. They are often twisted and are remarkably long 20-45 cm (8-18") in length. It is one of the two southern pines with long needles, the other being Slash Pine.
The cones, both male (catkins) and female (cones), are initiated during the growing season before buds emerge. Male cones begin forming in their buds in July, while female conelets are shaped during a relatively short period of time in August. Pollination occurs early the next spring, with the male cones 3-8 cm (1-3") long. The female (seed) cones mature in about 20 months from pollination; when grown-up they are yellow-brown in color, 15-25 cm long, 5-7 cm broad opening to 12 cm (6-10" long, 2-2½" broad opening to 5" broad), and have a small but sharp downward-pointing spine on the middle of each scale. The seeds are 7-9 mm long, with a 25-40 mm wing (1/3" long, with a 1 - 1¾" wing).
Longleaf Pine takes 100 to 150 years to turn out to be full size and can live to 300 years old. When young, they grow a long taproot, which is frequently 2-3 m (6-10 ft) long; by maturity they have a wide spreading lateral root system with several deep 'sinker' roots. It grows on well-drained, regularly sandy soil, often in pure stands. The scientific name meaning "of marshes" is a misunderstanding on the part of Philip Miller who described the species, from seeing Longleaf Pine forests with temporary winter flooding.Longleaf Pine is also known as Southern Yellow Pine or Longleaf Yellow Pine, and in the past as Pitch Pine (dropped as it caused confusion with Pitch Pine, Pinus rigida). Long leaf pines are found in the upland pine forest habitat