''Picea chihuahuana'', the Chihuahua spruce, is a medium-sized

evergreen In botany, an evergreen is a plant which has Leaf, foliage that remains green and functional throughout the year. This contrasts with deciduous plants, which lose their foliage completely during the winter or dry season. Consisting of many diffe ...

tree In botany, a tree is a perennial plant with an elongated stem, or trunk, usually supporting branches and leaves. In some usages, the definition of a tree may be narrower, e.g., including only woody plants with secondary growth, only ...

growing to 25–35 m tall, and with a trunk diameter of up to 1 m. It is native to northwest

Mexico Mexico, officially the United Mexican States, is a country in North America. It is the northernmost country in Latin America, and borders the United States to the north, and Guatemala and Belize to the southeast; while having maritime boundar ...

, where it occurs in 25 small populations in the

Sierra Madre Occidental The Sierra Madre Occidental is a major mountain range system of the North American Cordillera, that runs northwest–southeast through northwestern and western Mexico, and along the Gulf of California. The Sierra Madre is part of the American C ...

mountains in Chihuahua and

Durango Durango, officially the Free and Sovereign State of Durango, is one of the 31 states which make up the Political divisions of Mexico, 32 Federal Entities of Mexico, situated in the northwest portion of the country. With a population of 1,832,650 ...

. It grows at moderate altitudes from 2300–3200 m, growing along streamsides in mountain valleys, where moisture levels in the soil are greater than the otherwise low rainfall in the area would suggest. The

bark Bark may refer to: Common meanings * Bark (botany), an outer layer of a woody plant such as a tree or stick * Bark (sound), a vocalization of some animals (which is commonly the dog) Arts and entertainment * ''Bark'' (Jefferson Airplane album), ...

is thin and scaly, flaking off in small circular plates 5–10 cm across. The crown is conic, with widely spaced branches with drooping branchlets. The shoots are stout, pale buff-brown, glabrous, and with prominent pulvini. The

leaves A leaf (: leaves) is a principal appendage of the stem of a vascular plant, usually borne laterally above ground and specialized for photosynthesis. Leaves are collectively called foliage, as in "autumn foliage", while the leaves, stem, ...

are needle-like, 17–23 mm long, stout, rhombic in cross-section, bright glaucous blue-green with conspicuous lines of

stomata In botany, a stoma (: stomata, from Greek ''στόμα'', "mouth"), also called a stomate (: stomates), is a pore found in the epidermis of leaves, stems, and other organs, that controls the rate of gas exchange between the internal air spa ...

; the tip is viciously sharp. The

cones In geometry, a cone is a three-dimensional figure that tapers smoothly from a flat base (typically a circle) to a point not contained in the base, called the ''apex'' or '' vertex''. A cone is formed by a set of line segments, half-lines, ...

are pendulous, broad cylindrical, 7–12 cm long and 3 cm broad when closed, opening to 4–5 cm broad. They have stiff, bluntly rounded scales 1.5–2 cm broad, and are green, maturing pale brown 6–8 months after pollination. The

seed In botany, a seed is a plant structure containing an embryo and stored nutrients in a protective coat called a ''testa''. More generally, the term "seed" means anything that can be Sowing, sown, which may include seed and husk or tuber. Seeds ...

s are black, 4 mm long, with a 10–13 mm long pale brown wing. Chihuahua spruce was only discovered in 1942 by the Mexican

botanist Botany, also called plant science, is the branch of natural science and biology studying plants, especially Plant anatomy, their anatomy, Plant taxonomy, taxonomy, and Plant ecology, ecology. A botanist or plant scientist is a scientist who s ...

Maximino Martínez, and is

endangered An endangered species is a species that is very likely to become extinct in the near future, either worldwide or in a particular political jurisdiction. Endangered species may be at risk due to factors such as habitat loss, poaching, inv ...

with just 25 small populations, none comprising more than a few hundred trees. It is related to Martinez Spruce from northeast Mexico, but differs in the shorter, blue-green leaves, and the smaller, narrower cones with smaller scales. No other related spruces are found in

North America North America is a continent in the Northern Hemisphere, Northern and Western Hemisphere, Western hemispheres. North America is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South Ameri ...

, with its next-closest relatives in eastern

Asia Asia ( , ) is the largest continent in the world by both land area and population. It covers an area of more than 44 million square kilometres, about 30% of Earth's total land area and 8% of Earth's total surface area. The continent, which ...

. It is a very attractive tree and is starting to be planted as an ornamental tree in botanical gardens, particularly valued in warm areas as it is one of the most heat-tolerant of all spruces, more tolerant of summer heat than

Blue Spruce The blue spruce (''Picea pungens''), also commonly known as Colorado spruce or Colorado blue spruce, is a species of spruce tree native to North America in Arizona, Colorado, Idaho, New Mexico, Utah and Wyoming. It is noted for its blue-green co ...

, which it resembles in foliage.

References

External links

Gymnosperm Database
{{Taxonbar, from=Q1072578 chihuahuana Endemic flora of Mexico Trees of Northern America Endangered plants Flora of the Sierra Madre Occidental