Pinus strobiformis Engelm.

  • Authority

    Farjon, Aljos K. & Styles, Brian T. 1997. Pinus (Pinaceae). Fl. Neotrop. Monogr. 75: 1-291. (Published by NYBG Press)

  • Family

    Pinaceae

  • Scientific Name

    Pinus strobiformis Engelm.

  • Type

    Type. Mexico. Chihuahua: Cosiquiriachi, Oct 1846, Wislizenus 231 (holotype, MO; isotype, MO).

  • Synonyms

    Pinus ayacahuite subsp. strobiformis (Engelm.) A.E.Murray, Pinus bonapartea Roezl, Pinus ayacahuite var. brachyptera Shaw, Pinus strobiformis var. carvajalii Silba, Pinus strobiformis var. potosiensis Silba, Pinus ayacahuite var. novogaliciana Carvajal

  • Description

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    Species Description - Tree, medium to tall, height to 25-30 m, dbh to 80-100 cm. Trunk monopodial, straight, erect. Bark thick, rough and scaly, fissured, breaking into small, irregular plates, dark brown, weathering grey; on young trees and branches thin, smooth, silvery-grey. Branches of first order whorled, moderately long, spreading horizontally or assurgent, of higher orders long, slender, flexible, curved down, ultimately assurgent. Crown conical or pyramidal in young trees, becoming more rounded or irregular in older trees. Shoots smooth, puberulous or glabrous, with prominent, small, short decurrent pulvini, pale reddish brown. Cataphylls small, 5-10 mm long, subulate, brown with erose-hyaline margins, soon deciduous (falling well before leaf fascicles). Vegetative buds ovoid to ovoid-oblong, the terminal bud 8-15 X 58 mm, the laterals smaller, not or only slightly resinous; the scales free, spreading, subulate, reddish brown with erose-hyaline margins. Fascicle sheaths 20-25 mm long, consisting of ca. 6-8 loosely imbricate, papery, orange-brown scales with hyaline margins, soon disintegrating and deciduous at the end of the growing season. Leaves in fascicles of 5, very rarely 6, in dense tufts toward the ends of ultimate branches, persisting 3-5 years, lax, straight or slightly curved proximally, sometimes slightly twisted, spreading at various angles from the shoot (usually 40-60°), (5-)7-11 (-12) cm X (0.6-)0.8-1.1 (-1.2) mm, with remotely (rarely more densely) serrulate or nearly entire margins, acute, dark green to glaucous-green. Stomata: Leaves commonly epi-stomatic, sometimes weakly amphistomatic with a few intermittent lines of stomata on the abaxial side, rarely amphistomatic with ca. 4 lines of stomata on each face. Leaf anatomy: Cross section triangular, the abaxial side slightly convex; epidermis thick; hypodermis thin, unilayered; resin ducts (1-)2-5, external, rarely 1 medial, mostly situated on the abaxial side; stele terete; outer walls of endodermal cells not thickened; vascular bundle I, oval in cross section. Pollen cones crowded on the proximal part of new shoots, spreading, subtended by light brown, scarious bracts, ovoid-oblong to short cylindrical, 610 mm long, yellow, maturing to orange-brown. Seed cones subterminal, axillary, solitary or in pairs or sometimes whorls of 3-4 on stout, 15-25 mm long peduncles, at first erect, becoming pendulous and falling with the peduncle attached. Immature cones elliptic to short cylindrical, greenish purple, soon light brown, maturing in two seasons. Mature cones variable, mostly cylindrical or broad cylindrical to ovoid-oblong when opened, long cones usually slightly curved, 12-30(-60) X 7-11 cm when open. Seed scales ca. 70-120, spreading obliquely to patent, the basal scales recurved or reflexed, the scales at mid-cone straight (the apophyses usually recurved or reflexed), obtrullate, with curved margins, thick woody, of similar shape around the cone but differentiating from base to apex, often longitudinally furrowed on both sides, with one or two deep seed cavities adaxially, reddish brown to purplish brown, with very small or virtually absent marks of seed wings. Apophysis more or less cuneate or elongated, thick at the proximal end, thinning out and straight, recurved or reflexed distally, smooth or longitudinally furrowed, often very resinous, light yellowish brown or dark ochraceous. Umbo terminal, broadly triangular, obtuse, 5-10 mm wide, greyish brown, usually covered with resin. Seeds (broadly) obovoid, slightly flattened, 12-18 X 8-11 mm, reddish brown or brown; commonly one of the seeds on a scale aborts. Seed wings adnate, vestigial to very small, up to ½ the length of the seed in some cones; aborted seeds usually have relatively large wings. Cotyledons 11-14, 30-40 mm long.

  • Discussion

    Uses. As one of the “soft pines,” P. strobiformis, often equated with P. ayacahuite in the vernacular of N Mexico (Pérez de la Rosa, 1993), is sought after by lumbermen, who consider its wood of good quality for carpentry work.

    Engelmann (1848) described P. strobiformis based on material gathered by F. Wislizenus on the “highest peaks about Cosihuiriachi” in Chihuahua. There are two sheets at MO of Wislizenus 231, of which MO-3377668 has been annotated by Engelmann; a third sheet (Wislizenus 155, only a seedling) has not been determined definitely by Engelmann and is not type material, as stated in Farjon (1993). As some authors (Shaw, 1909; Andresen & Steinhof, 1971) have pointed out, Engelmann apparently abandoned this name in his later publications, but as he did not indicate of what species he would have considered it to be a synonym, later treatments in synonymy with P. ayacahuite (Parlatore, 1868), or as a variety of it (Shaw, 1909), are to be credited to these authors only.

    Carvajal and McVaugh (1992) discuss the type specimen, Wislizenus 231 (MO), seen by McVaugh, and conclude that its differences with specimens of P. ayacahuite do “not seem to be enough to justify species status for P. strobiformis." Unfortunately, of the cone there is nothing but a single seed scale, mounted with the abaxial side up, and no seed. Their conclusion is based on the leaves of what amounts to a very incomplete collection. More material might have warranted a different conclusion; however, in this case the type collection does not suffice.

    Sargent (1897), after some earlier doubts, accepted P. strobiformis but based his concept of the species primarily on material from the most northern part of the range, Arizona and New Mexico. It is likely that, in fact, P. strobiformis sensu Sargent is synonymous in part with P. flexilis var. reflexa, as a preliminary survey by A. Farjon of specimens in A and US has indicated. Sudworth (1898), in a precursor to Little’s (1953; 1979) checklists, accepted P. strobiformis sensu Sargent, but extended its range to Mexico and Guatemala, thereby implicitly including P. ayacahuite. Little (1953) at first treated P. strobiformis Engelmann and its synonyms under P. flexilis var. reflexa, but after the work of Steinhoff and Andresen (1971) and Andresen and Steinhoff (1971), he reversed it and accepted P. strobiformis instead, with P. flexilis var. reflexa in synonymy. As has been argued under the latter taxon, the work of Andresen and Steinhoff hardly dealt with Mexican trees, and they seem to have ignored Shaw’s (1909) treatment. Their inclusion of P. ayacahuite Ehrenberg ex Schlechtendal (1838) in synonymy is certainly erroneous; they ought to have abandoned the binomial P. strobiformis Engelmann (1848) for their species on the basis of nomenclatural priority.

    As interpreted here, P. strobiformis, in accordance with its type, is the taxon Shaw (1909) accepted as P. ayacahuite var. brachyptera. It is more variable than Shaw could have known given the few collections he studied, but its ovuliferous cone and seeds are nevertheless distinct from P. flexilis as well as from P. ayacahuite. As pointed out in a recent morphometric study by Pérez de la Rosa (1993), the longer, usually epistomatic, serrulate leaves and the larger cones with usually elongated, recurved apophyses and rudimentary seed wings distinguish P. strobiformis from P. flexilis. Pinus ayacahuite has similar foliage, though slightly longer still, but its cones have thinner, flexible seed scales without marked seed cavities and with well-developed seed wings. The reduced and ineffective wing of the seed of P. strobiformis suggests a diversion from wind dispersal to animal vectors, which has been more fully completed in P. flexilis and is perfected in P. albicaulis, in which not only is wing development completely suppressed but the cones remain closed through ripening as well.

    Carvajal (1986) described a new species, P. novogaliciana, from W Jalisco, citing P. ayacahuite var. brachyptera Shaw, p.p. (excl. type), in synonymy. He failed to provide a Latin diagnosis. The same taxon was later validly published as a variety of P. ayacahuite by Carvajal and McVaugh (1992). As was there indicated, Brian Styles would have treated “this plant of western Jalisco under the name of Pinus strobiformis Engelm.,” which is maintained here. The remarkable large cones, given as up to 60 cm long, have rather thick woody scales with elongated and strongly recurved apophyses and virtually wingless seeds. We have not seen cones of that length, which may be exceptional.

    Rushforth (1987) commented on pines of which he had collected specimens on Cerro Potosi in Nuevo León under the name P. reflexa. It was his opinion that this pine “may not be the same as the one Engelmann described as a variety of P. flexilis, in which case a new name may be required.” Silba (1990) picked up the suggestion, virtually copied the description given by Rushforth, designated a type specimen from the same locality at NY, and named it P. strobiformis var. potosiensis. That the name P. reflexa “cannot be applied here as the type is from the Santa Rita Mountains of Arizona” is an invalid argument-a taxon need not be confined to its type locality. Study of more collections from Cerro Potosi reveals that there are possibly two related taxa there: P. flexilis var. reflexa and P. strobiformis. Accounts of cone variation may be due in part to introgression involving both taxa. Pinus strobiformis cones are remarkably wide but short (12-17 X 8-11 cm when open; Fig. 56Db) in the material collected by Stead and Styles from this mountain in 1980. Study of genetic variation and taxonomic relationships of the “White pines” occurring on Cerro Potosi and neighbouring mountains [see also Perry’s (1991) claim of “typical” P. flexilis found there] may turn out to be worthwhile. It seems premature, pending such a study, to propose any further new names for these pines.

    Finally, Perry (1991) treated P. strobiformis and P. ayacahuite var. brachyptera as two distinct but sympatric taxa, the former having shorter leaves and shorter cones than the latter. Since both names are based on the same type, they are nomenclaturally identical, and Perry should have adopted a different name for the latter instead of following Martínez (1948), who in turn adopted Shaw’s (1909) nomenclature. He mentions finding often trees with intermediate morphological characters and ascribes this to hybridization between the two, which, in our opinion, amounts to the conclusion that individuals belonging to one and the same species interbreed.

    Distribution and Ecology: United States: Arizona, New Mexico, rare in Trans-Pecos Texas. Mexico: In Sonora, Chihuahua, Coahuila, Nuevo León, Sinaloa, Durango, Jalisco, very local in Zacatecas and San Luís Potosí. Pinus strobiformis is a montane pine of mesic sites; its altitudinal range is 1900-3500 m. It occurs on sites with relatively deep, humus-rich though often rocky soils, especially on N-facing slopes or along mountain streams. It grows in small, pure stands within pine or pine-oak forest, but more commonly it is mixed with P. arizonica, P. engelmannii, P. leiophylla var. chihuahuana, P. durangensis, P. lumholtzii, and/or various species of Quercus and Arbutus. In a more mesic forest type, it is associated with Abies and Pseudotsuga, and at the highest altitudes with P. hartwegii; on Cerro Potosi it grows at the lower limits of the shrubby pine P. culminicola. The climate in the Sierra Madre Occidental is characterized by summer rains (thunderstorms) as well as winter precipitation; winter snows are common at the higher altitudes.

    Phenology: Dispersal of pollen occurs in May-June.

  • Distribution

    Mexico North America| Chihuahua Mexico North America| Coahuila Mexico North America| Durango Mexico North America| Jalisco Mexico North America| Nuevo León Mexico North America| San Luis Potosí Mexico North America| Sinaloa Mexico North America| Sonora Mexico North America|