Pinus maximartinezii Rzed.
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Authority
Farjon, Aljos K. & Styles, Brian T. 1997. Pinus (Pinaceae). Fl. Neotrop. Monogr. 75: 1-291. (Published by NYBG Press)
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Family
Pinaceae
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Scientific Name
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Type
Type. Mexico. Zacatecas: Sierra de Morones, Cerro de Pi nones, W of Pueblo Viejo, 25 Jan 1964, Rzedowski 18258 (holotype, MEXU; isotypes, ENCB, F, GH, INIF, K, MICH, P, US).
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Description
Species Description - Tree, small to medium, height to 5-10(-15) m, dbh to 40-50 cm. Trunk monopodial, short, branching low, often contorted or curved. Bark relatively thick on the lower trunk, thin elsewhere, smooth but eventually rough, tessellated into square, ca. 10 cm wide plates, inner bark orange-brown to reddish brown, outer bark grey. Branches of first order often numerous, long, ascending to erect in the top, the lower branches spreading; branches of higher orders long and flexible, those bearing cones becoming pendulous. Shoots slender, slow-growing, glabrous or with puberulent bases of fascicles, with small, non-decurrent pulvini, initially glaucous or greyish green, turning orange-brown to grey. Leaves do not grow in flushing shoots until these have reached their full length, ca. 10 cm. Cataphylls small, ca. 5 mm long, narrowly triangular-caudate, recurved, with erose-ciliate margins and an elevated midvein, soon deciduous. Vegetative buds small, ovoid-conical, the terminal buds 5-8 mm long, the laterals smaller, resinous; the scales imbricate, appressed, subulate, light brown. Fascicle sheaths 7-8 mm long, light brown; the outer scales deciduous, the inner scales recoiling, semi-persistent, forming a small rosette at the base of the fascicle. Leaves in fascicles of 5, very rarely 3 or 4, in dense tufts near the ends of long, slender branches, persisting two years, straight, lax, spreading at 30-70° from the shoot, 7-11 (-13) cm X 0.5-0.7 mm, with entire (rarely a few minute teeth) margins, acute, glaucous green, in some trees green, the two adaxial faces often whitish. Stomata only on the adaxial faces, in 2-3(-4) lines on each face; the slightly convex abaxial face has two faint grooves corresponding with the underlying resin ducts. Leaf anatomy: Cross section triangular, with a slightly convex abaxial side; hypodermis uniform, with 1-2 layers of cells; resin ducts usually 2, external, on the abaxial side; stele terete; outer walls of endodermal cells not thickened; vascular bundle single, usually with a median wall of reinforcing cells in the phloem. Pollen cones crowded on the proximal half of flushing shoots, forming an elongated “spike," ovoid-oblong, 8-10 mm long, yellowish. Seed cones lateral, solitary on ultimate branches, on a very short peduncle or almost sessile (a lateral shoot usually grows with an angle from the near base of the cone). Immature cones large, ovoid-truncate, green until full-grown, maturing in 18-24 months or perhaps longer. Mature cones broadly ovoid-truncate, widest slightly below the middle, (15-) 17-25(-27) X 10-15 cm when the scales have parted. Seed scales ca. 80-110, parting slowly, the distal scales more than the proximal scales, usually insufficiently wide to release the seeds, very thick woody, rigid, obtrullate, tapering toward the very thick rachis, up to 50 mm wide below the apophysis, of similar shape around the cone but differentiating from base to apex, with deep seed cavities on the adaxial side, reddish brown. Apophysis very prominent, 35-50 X 20-35 mm, rhombic-pyramidal at mid-cone, usually straight, transversely keeled, the upper margin angular, those on the proximal and distal scales narrowly conical, often curved, dull light brown or reddish brown, often resinous. Umbo dorsal, obtuse-triangular or rhombic-pyramidal, 5-10 X 10-18 mm, sometimes with a minute prickle, concolorous or grey-brown. Seeds oblong or ovoid-oblong, slightly flattened, 2028 X (8-) 10-12 X 7-10 mm, wingless when the seed is disconnected from the cup-like depression in the scale, but on one side of the seed rudiments of a wing may be present. Integument ca. 2 mm thick, very hard, yellowish brown or greyish brown. Seedlings large, with 18-24 cotyledons; juvenile leaves curved, flattened, ca. 8 cm long, silvery-blue, persisting well beyond the development of adult leaves, sometimes up to 20 years (Muir, 1992).
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Discussion
Uses. Like other “piñones" (pinyon pines) in Mexico, this species is of local importance for its edible seeds, which are harvested by local people and marketed in the region. Due to its low stature and branching of the trunk, its timber is not used. The species is considered endangered (Farjon et al., 1993) due to fire and grazing hazards resulting in few seedlings that succeed in establishing themselves. Although there is an awareness amongst botanists and foresters in Mexico of its importance, current in situ protection (fire prevention and fire fighting) seems inadequate to ensure long-term preservation of this interesting narrow endemic (Farjon, 1994). Carvajal and McVaugh (1992) gave an account of the discovery of Pinus maximartinezii by Jerzy Rzedowski in 1963, which was triggered by an observation of abnormally large pinyon seeds offered for sale on a local market. Although it shares several characters with P. cembroides (pinyon pine)—some of which are synapomorphies but others, such as the “wingless” seed, more likely the result of convergent evolution—it is very distinct in others. Pinus maximartinezii has the highest number of cotyledons of all pines (and of conifers in general). There is the peculiar median wall of sclerenchymatous cells in the phloem of the single vascular bundle in the leaves, noted by Rzedowski (1964), which he interpreted as a trait showing intermediacy between diploxyl (ancestral) and haploxyl (derived) leaves in pines. Its exceptionally large and heavy seed cones (up to 2 kg when full-grown) are unlike those of P. cembroides and its allied taxa, but resemble those of P. gerardiana of Afghanistan and Pakistan, which also has similar seeds. Zavarin and Snajberk (1987) report similarity in monoterpene composition with P. pinceana and dissimilarity with P. culminicola, one of the other “pinyons” studied. Pinus culminicola is closely related to P. cembroides and its allied taxa (Malusa, 1992; this study). A preliminary investigation of cpDNA differentiation in Mexican Pinus species (Pérez de la Rosa et al., 1995) appears to confirm dissimilarity with P. cembroides, as does the cladistic analysis of morphological data by Malusa (1992), while it shows that there may indeed be some relationship with P. pinceana. These recent investigations show that sect. Parryanae, as traditionally circumscribed (Little & Critchfield, 1969; Far-jon, 1984), is a heterogeneous and probably artificial group. It also has become increasingly apparent that the “pinyon pines” (subsect. Cembroides) are not monophyletic (Malusa, 1992; Pérez de la Rosa et al., 1995; this study) and are in need of a comprehensive revision.
Mexico: In S Zacatecas, where it is restricted to a limited area of 5-10 km2 in scattered stands on the summit ridges and E slopes of the Sierra de Morones, from ca. 12 km SW to a few km W of Juchipila. The main area is locally known as Cerro de Piñones and lies a few kilometres W of Pueblo Viejo, a small village at the E base of the mountains. Due to limited botanical exploration of this part of Mexico and the likelihood that similar ecological conditions occur on other “mesas" in the region, future finds of other populations cannot be ruled out. The rock of this mountain is in part sandstone or limestone and also metamorphic, the soils are very rocky and shallow. Precipitation is probably ca. 700-800 mm annually, virtually restricted to four months in the summer. Pinus maximartinezii is virtually the only pine here, but a few scattered individuals of P. leiophylla var. chihuahuana have been seen by us. Its altitudinal range is 1800-2400 m. Abundant are various large-leaved species of deciduous Quercus such as Q. macrophylla, which are bare during the long dry season from September to May. Fires occur regularly in the region in all vegetation types; it is not known whether this species is adapted well to reseed itself after fire.
Phenology: Pollen dispersal is usually in May-June; the ovuliferous cones take 18-24 months to reach maturity and perhaps longer for the seeds to ripen fully, which mostly remain in the cones. Squirrels are capable of biting off the apohyses to reach the seeds and probably store them. They, and probably birds, may play a crucial role in effective seed dispersal, but this has not been investigated to date.
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Distribution
Mexico North America| Zacatecas Mexico North America|