Pinus lawsonii / Lawson's pine

subgenus Pinus, section Trifoliae (Duhamel), subsection Australes (Loudon).

Pinus lawsonii, first described in 1862 by Benedikt Roezl (1823–1885) ex George Gordon (1806–1879) et Robert Glendinning (1844 - 1928) is commonly known as Lawson's pine, as well as, Pino ortigillo in the Spanish language. The species name honors Scottish nurseryman, Charles Lawson (1794 - 1873), who, in his nursery in Edinburgh, grew many conifers sourced from western American seed, most notably Chamaecyparis lawsoniana.

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Description. Lawson's pine is an evergreen, coniferous species of tree that grows to mature heights of 100 feet (30 m) with a single straight trunk up to 30 inches (75 cm) in diameter, measured at breast height; and a domed, open, often irregular crown.
Bark is thin, colored red-brown, exfoliating in thin plates; with age, becoming thick, rough, scaly, black-brown with deep longitudinal fissures and a purplish-red inner bark.
 	Shoots are smooth, ridged, colored orange-brown, and often glaucous. Foliar units form dense to open tufts.
 	Fascicle sheaths at first are up to 1 inch (25 mm) long, with imbricate, lustrous orange-brown scales. Sheaths are persistent, but reduced to 0.4 to 0.6 inch (10 - 15 mm) long in older fascicles, weathering grey or blackish brown.
 	Leaves (needles) are borne grow in fascicles of of 3 to 4 (sometimes 5), persisting 2-3 years on the tree. Individual needles are straight, directed forward to spreading wide, stiff, measuring 4.8 to 6 inches (12 - 20 cm) long by 0.04 to 0.048 inch (1 - 1.2) mm) thick, colored glaucous green, with an acute apex. Bands of stomata appear on all faces of the leaves, 9 to 12 lines on the convex outer face and 4 to 5 lines on each inner face.
 	Pollen cones grow crowded near the basal end of a new shoot, ovoid-oblong to cylindrical shaped, measuring 0.4 to 0.8 inch (10 - 20 mm) long, colored yellowish green, turning light brown.
 	Seed cones develop near the base of new shoots, growing solitary or opposite on stout, curved peduncles up to 0.4 inch (10 mm) long, which usually fall with the cone. First-year cones appear purplish red, 0.4 to 0.6 inch (10 - 15 mm) long, maturing in their second year. Mature cones are ovoid shaped with a flattened base when open and measure 2 to 3.2 inches (5 - 8 cm) long by 1.6 to 2.4 inches (4 - 6 cm) wide.
 	Seed scales number 70 - 100, and are thick, woody, colored dark brown, with two light brown marks of seed wings on the upper side. Apophysis is slightly raised, transversely keeled, with a rhombic outline. Umbo is dorsal, pyramidal, curved, transverse·rhombic, measuring 0.12 to 0.16 inch (3 - 4 mm) by 0.16 to 0.2 inch (4 - 5 mm), colored grey-brown, without a prickle.
 	Seeds are flattened-obovoid shaped, 0.16 to 0.2 inch (4 - 5 mm) long, colored dark brown with a 0.48 to 0.64 (12 - 16 mm) long, translucent light-brown wing.
Distribution. This species is native to Mexico — Michoacán, México, Morelos, Distrito Federal, Veracruz (one locality), Guerrero, and Oaxaca; occurring in forest and woodland at elevations of 4,300 to 8,600 feet (1,300 - 2,600 m) above sea level where climate is warm-temperate to temperate with 24 to 60 inches (600 - 1,500 mm) annual precipitation and a November to May dry season. It grows with various species of Quercus and a variety of other pines including Pinus pringlei. P. patula, P. montezumae, P. oocarpa, P. leiophylla, P. herrerae, P. teocote, and P. pseudostrobus. On sites with sandy, shallow soil, Juniperus can be co-dominant.
Hardy to USDA Zone 10 — cold hardiness limit between 30° and 40°F (-1° and +4.4°C).
Description. Lawson's pine is an evergreen, coniferous species of tree that grows to mature heights of 100 feet (30 m) with a single straight trunk up to 30 inches (75 cm) in diameter, measured at breast height; and a domed, open, often irregular crown. Bark is thin, colored red-brown, exfoliating in thin plates; with age, becoming thick, rough, scaly, black-brown with deep longitudinal fissures and a purplish-red inner bark. Shoots are smooth, ridged, colored orange-brown, and often glaucous. Foliar units form dense to open tufts. Fascicle sheaths at first are up to 1 inch (25 mm) long, with imbricate, lustrous orange-brown scales. Sheaths are persistent, but reduced to 0.4 to 0.6 inch (10 - 15 mm) long in older fascicles, weathering grey or blackish brown. Leaves (needles) are borne grow in fascicles of of 3 to 4 (sometimes 5), persisting 2-3 years on the tree. Individual needles are straight, directed forward to spreading wide, stiff, measuring 4.8 to 6 inches (12 - 20 cm) long by 0.04 to 0.048 inch (1 - 1.2) mm) thick, colored glaucous green, with an acute apex. Bands of stomata appear on all faces of the leaves, 9 to 12 lines on the convex outer face and 4 to 5 lines on each inner face. Pollen cones grow crowded near the basal end of a new shoot, ovoid-oblong to cylindrical shaped, measuring 0.4 to 0.8 inch (10 - 20 mm) long, colored yellowish green, turning light brown. Seed cones develop near the base of new shoots, growing solitary or opposite on stout, curved peduncles up to 0.4 inch (10 mm) long, which usually fall with the cone. First-year cones appear purplish red, 0.4 to 0.6 inch (10 - 15 mm) long, maturing in their second year. Mature cones are ovoid shaped with a flattened base when open and measure 2 to 3.2 inches (5 - 8 cm) long by 1.6 to 2.4 inches (4 - 6 cm) wide. Seed scales number 70 - 100, and are thick, woody, colored dark brown, with two light brown marks of seed wings on the upper side. Apophysis is slightly raised, transversely keeled, with a rhombic outline. Umbo is dorsal, pyramidal, curved, transverse·rhombic, measuring 0.12 to 0.16 inch (3 - 4 mm) by 0.16 to 0.2 inch (4 - 5 mm), colored grey-brown, without a prickle. Seeds are flattened-obovoid shaped, 0.16 to 0.2 inch (4 - 5 mm) long, colored dark brown with a 0.48 to 0.64 (12 - 16 mm) long, translucent light-brown wing. Distribution. This species is native to Mexico — Michoacán, México, Morelos, Distrito Federal, Veracruz (one locality), Guerrero, and Oaxaca; occurring in forest and woodland at elevations of 4,300 to 8,600 feet (1,300 - 2,600 m) above sea level where climate is warm-temperate to temperate with 24 to 60 inches (600 - 1,500 mm) annual precipitation and a November to May dry season. It grows with various species of Quercus and a variety of other pines including Pinus pringlei. P. patula, P. montezumae, P. oocarpa, P. leiophylla, P. herrerae, P. teocote, and P. pseudostrobus. On sites with sandy, shallow soil, Juniperus can be co-dominant. Hardy to USDA Zone 10 — cold hardiness limit between 30° and 40°F (-1° and +4.4°C).

Attribution from: Aljos Farjon and B.T. Styles; Pinus (Pinaceae); ©1997, Flora Neotropica Monograph 75, The New York Botanical Garden, New York, NY.

Pinus lawsonii — a mature tree in habitat.
Photo by C.J. Earle
Copyright 2005 Chris Earle all rights reserved
Pinus lawsonii — a forest on a hillside above Oaxaca valley.
Photo by C.J. Earle
Copyright 2005 Chris Earle all rights reserved
Pinus lawsonii — bark detail.
Photo by C.J. Earle
Copyright 2005 Chris Earle all rights reserved
Pinus lawsonii — a mature seed cone in situ.
Photo by C.J. Earle
Copyright 2005 Chris Earle all rights reserved

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