Pinus rzedowskii Madrigal & M.Caball.

  • 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 rzedowskii Madrigal & M.Caball.

  • Type

    Type. Mexico. Michoa-cán:  Puerto del Pinabete, ca. 47 km W of Dos Aguas, 25 Nov 1968, Madrigal 5. 2202 (holotype, INIF; isotypes, ENCB, GH, MEXU, MICH).

  • Description

    Species Description - Tree, medium or rarely tall, height to 15-30 m, dbh to 30-60 cm. Trunk monopodial, erect, often curved or contorted, with a partly clear bole only when growing among other trees in a forest stand. Bark up to 5-6 cm thick on the lower part of larger trunks, rough and scaly, breaking into large, exfoliating plates divided by deep, longitudinal fissures, dark brown, weathering grey; on young trees and branches rough and scaly, exfoliating in thin plates, more or less smooth (but not as in species of sect. Strobus) in highest-order branches, reddish brown or grey-brown. Branches of first order long, whorled in young trees, spreading and ascending, often contorted, persistent; branches of higher orders slender, flexible. Crown pyramidal in young trees, open and irregular in old trees. Shoots slender, smooth, with weakly developed, transversely ridged pulvini, greyish. Cataphylls small, ca. 5 mm long, fragile, subulate, with erose-hyaline margins, soon deciduous. Vegetative buds ovoid-oblong, the terminal buds 8-10 X 4-5 mm, the laterals of nearly equal size, not resinous; the scales imbricate, small, subulate, with ciliate margins and spreading, reddish brown apices. Fascicle sheaths of young leaves 7-9 mm long, with soon spreading, yellowish to reddish brown scales; scales of mature fascicles recoiling, forming a rosette at the base of the fascicle, finally deciduous before the fascicles. Leaves in fascicles of (3-)4-5, in dense, lax tufts persisting 2-3 years on the branchlets, straight or slightly reflexed, not drooping, 6-10 cm X 0.6-0.8 mm, with irregularly serrulate margins, acute-acuminate, yellowish green or greyish green, weakly glaucous on the adaxial faces. Stomata on the two adaxial faces only, with 3-4 (intermittent) lines of stomata on each face (2 grooves corresponding with resin ducts on the abaxial face). Leaf anatomy: Cross section triangular or transverse-triangular, with a convex abaxial side; hypodermis unilayered, thin, rarely with some additional cells; resin ducts 2-4, external, 2(-3) on the abaxial side and sometimes 1-2 additionally on one or both adaxial sides; stele terete; endodermal cells large but thin-walled; vascular bundle 1. Pollen cones crowded, spirally arranged, after shoot elongation forming a 5-7 cm long "spike" leaving the shoot base and apex free, small, 5 x 3 mm, purplish, turning brown. Microsporophylls peltate, 0.5 mm wide, with denticulate upper margin. Seed cones lateral on ultimate branches, solitary or in whorls of 2-4 on 15-30 mm long, slender, slightly curved, remotely bracteate peduncles which fall with the cones. Immature cones ovoid, 10-15 X 8-12 mm, with prominent, transversely keeled umbos, purplish, turning green when growing, maturing in two seasons. Mature cones ovoid to ovoid-conical when closed, ovoid when opened, usually symmetrical, slightly flattened at base, 10-15 X 6-8.5 cm when open, very resinous. Seed scales ca. 80-120, parting to release the seeds, spreading at 40-50° from the axis, thin woody, rigid, oblong, with parallel or slightly undulating margins, concavo-convex, often wider (up to ca. 20 mm) than the apophysis, light brown or orange-brown abaxially, idem with orange-brown marks of seed wings on the adaxial side. Apophysis prominent, similarly shaped around the cone, transversely keeled, rhombic or pentagonal in outline, upper margin angular, on proximal scales recurved, yellowish green turning ochraceous or light brown, often secreting yellowish resin. Umbo dorsal, rhombic-pyramidal, transversely keeled, 5-7 mm wide, obtuse or with a minute prickle, grey-brown. Seeds obovoid, (6-)8(-10) X (4-)5-6 mm, dark brown. Seed wings articulate, effective, held to the seed by two claw-like appendages, obliquely oblong, with a straight side, 20-30(-35) X 8-13 mm, brown, partly translucent, with darker stripes. Cotyledons (9-) 10-12(-14). * Remarks. The leaves do not elongate and remain as small buds covered by cataphylls in flushing shoots until the shoots have reached their full length of 5-7 cm. In the protologue (Madrigal & Caballero, 1969) a leaf width of 0.7-1 mm is mentioned, but neither in the type collection nor in any others here studied does the observed width exceed 0.8 mm.

  • Discussion

    Uses. No logging of this rare pine seems to take place, probably because of the inaccessibility of its populations in remote locations and the poor form of most trees from a lumberman’s viewpoint. Mexican botanists and (regional) foresters are apparently aware of the uniqueness of this species, but it has not received a protected status. Studies in population dynamics related to environmental factors, especially fire and reproduction, are much wanted to ensure proper management of this evolutionarily interesting pine. It was classified as endangered (IUCN-SSC, Farjon et al., 1993).

    This remarkable species was discovered in 1966 and botanical specimens were collected in 1968 in the NW part of the Sierra Madre del Sur in Michoacan. Its rarity and the difficult access to the three small localities now known, far from any paved roads, have been the main causes for its late discovery.

    Taxonomically, Pinus rzedowskii is one of the most interesting species in the genus. It is classified as a species in subgen. St robus. Its foliar morphology and anatomy places it close to P. cembroides and P. maximartinezii. Preliminary results from the analysis of cpDNA of a limited number of Mexican pine species (Pérez de la Rosa et al., 1995) place it and P. cembroides as unresolved clades away from P. maximartinezii and other species in subgen. Strobus. The elongation of shoots prior to leaf development is shared with P. maximartinezii; this phenomenon is more weakly developed in other pinyon pines. The bark of P. rzedowskii is unlike any other in Strobus and at least externally resembles that of species in subgen. Pinus. A more detailed comparative study would be desirable here, using more precisely defined methods and terminology than is customarily found in bark descriptions (Junnika, 1994). The seed cones and seeds are morphologically more similar to some species in subgen. Pinus. The growth of the apophysis, as deduced from the observation of cones at some different stages of development, and its final shape are reminiscent of P. merkusii, a very distinct SE Asian pine in subgen. Pinus. The seeds are likewise small, with we 11-de vel oped, articulate wings 3-4 times larger than the seeds. In this respect there is no resemblance to either P. cembroides or P. maximartinezii, nor to any other pinyon pine, in which the seeds are large and the wings vestigial.

    There is possibly an element of convergence involved in the evolution of the seed characters, and in conjunction with it some cone characters, when it is taken into account that these characters are related to seed dispersal strategies, which in the case of seedless wings coevolved with animal vectors, especially corvid birds (e.g., Lanner, 1982; Mattes, 1994). Genetically more-distant species could therefore have evolved similar cone/seed characters and vice versa. More phylogenetic work, using all available informative characters, is needed before one can adopt newly proposed classifications, such as a new subsection Rzedowskianae in (a polyphyletic) section Parryanae (Carvajal, 1986), which at this moment merely serves as a statement that it is somehow distinct.

    Distribution and Ecology: Mexico: Michoacán: In three disjunct localities in the district of Coalcomán, one near the village of Dos Aguas and the others approximately 40 km to the west. The two smaller populations, Cerro Chiqueritas and Cerro Ocotoso, are on steep talus of large, eroded limestone blocks, near the summits of small mountains in the mainly volcanic Sierra Madre del Sur. Each has only a few score trees, from old to saplings. The larger population is on more level ground, in an area known locally as Puerto del Pinabete, also with limestone boulders but interspaced with other substrates. In the two former areas, the trees remain small, <15 m tall; in Puerto del Pinabete trees to 30 m have been found. The altitudinal range is 2100-2400 m. Annual precipitation is ca. 1500 mm, most of it occurring from June to October. The climate is warm temperate, with a minimum of -5°C (December) and a maximum of 30°C (April). Although surrounded by extensive mixed pine forest with species like Pinus pseudostrobus, P. herrerae, and P. oocarpa, these species do not grow on the limestone talus. There, Quercus and shrubs such as Clusia Salvinii form an understorey with Agave and tall herbs. Fires occur frequently, but rejuvenation seemed good at least at Cerro Chiquerita, visited by A. Farjon in 1994.

    Phenology: Pollen dispersal is in April-May, at the end of the dry season.

  • Distribution

    Mexico North America| Michoacán Mexico North America|