Colorado pinyon

Description

Pinus edulis, the Colorado pinyon, two-needle piñon, pinyon pine, or simply piñon,is a pine in the pinyon pine group whose ancestor was a member of the Madro-Tertiary Geoflora (a group of drought resistant trees) and is native to the United States. The piñon pine (Pinus edulis) is a small to medium size tree, reaching 10–20 feet (3.0–6.1 m) tall and with a trunk diameter of up to 80 centimetres (31 in), rarely more. The bark is irregularly furrowed and scaly. The leaves ('needles') are in pairs, moderately stout, 3–5.5 cm (1+1⁄8–2+1⁄8 in) long, and green, with stomata on both inner and outer surfaces but distinctly more on the inner surface forming a whitish band. The cones are globose, 3–5 cm (1+1⁄4–2 in) long and broad when closed, green at first, ripening yellow-buff when 18–20 months old, with only a small number of thick scales, with typically 5–10 fertile scales. The cones open to 4–6 cm (1+1⁄2–2+1⁄4 in) broad when mature, holding the seeds on the scales after opening. The seeds are 10–14 mm (3⁄8–9⁄16 in) long, with a thin shell, a white endosperm, and a vestigial 1–2 mm (1⁄32–3⁄32 in) wing. The species intermixes with Pinus monophylla sbsp. fallax (see description under Pinus monophylla) for several hundred kilometers along the Mogollon Rim of central Arizona and the Grand Canyon resulting in trees with both single- and two-needled fascicles on each branch. The frequency of two-needled fascicles increases following wet years and decreases following dry years. The internal anatomy of both these needle types are identical except for the number of needles in each fascicle suggesting that Little's 1968 designation of this tree as a variety of Pinus edulis is more likely than its subsequent designation as a subspecies of Pinus monophylla based entirely upon its single needle fascicle.