Part II Classification of the Species
The following classification is based on the gradual evolution of the fruit from a cone symmetrical in form, parenchymatous in tissue, indehiscent and deciduous at maturity, releasing its wingless seed by disintegration—to a cone oblique in form, very strong and durable in tissue, persistent on the tree, intermittently dehiscent, releasing its winged seeds partly at maturity, partly at indefinite intervals during several years. This evolution embraces two extreme forms of fruit, one the most primitive, the other the most elaborate, among Conifers.
Two sections of the genus, Soft and Hard Pines, are distinguished by several correlated characters, and moreover are distinct by obvious differences in the tissues of their cones as well as in the quality and appearance of their wood.
With the Soft Pines the species group naturally under two subsections on the position of the umbo, the anatomy of the wood and the armature of the conelet. In one subsection (Cembra) are found three species, P. cembra and its allies, with the cone-tissues so completely parenchymatous that the cones cannot release the seeds except by disintegration. In both subsections there is a gradual evolution from a wingless nut to one with an effective wing, adnate in one subsection, adnate and articulate in the other. The different stages of this evolution are so distinct that the Soft Pines are easily separated into definite groups.
Among the Hard Pines a few species show characters that are peculiar to the Soft Pines. These exceptional species form a subsection (Parapinaster) by themselves.
With the remaining species, the majority of the Pines, the distinctions that obtain among Soft Pines have disappeared. The dorsal umbo, the articulate seed-wing, the persistent fascicle-sheath, the dorsal and ventral stomata of the leaf and its serrate margins, the dentate walls of the ray-tracheids have become fixed and constant. But a new form of seed-wing appears, with a thickened blade, assuming such proportions in P. Sabiniana and its two allies that these three constitute a distinct group, remarkable also for the size of its cones.
Here also appear a new form of fruit, the oblique cone, and a new method of dissemination, the serotinous cone. Associated with the latter are the persistent cone and the multinodal spring-shoot. These characters do not develop in such perfect sequence and regularity that they can be employed for grouping the species without forcing some of them into unnatural association. The oblique cone first appears sporadically here and there and without obvious reason. The persistent cone, the first stage of the serotinous cone, is equally sporadic in the earlier stages of evolution. The same may be said of the multinodal shoot.
Nevertheless these characters show an obvious progression toward a definite goal, where they are all united in a small group of species remarkable for the form and texture of their cones, for a peculiar seed-release and for the vigor and rapidity of their growth. It is possible, with the assistance of other characters, to segregate these species in three groups in which the affinities are respected and the general trend of their evolution is preserved.
The first group, the Lariciones, contains species with large ray-pits, cones dehiscent at maturity, and uninodal spring-shoots. They are, with two exceptions, P. resinosa and P. tropicalis, Old World species.
The second group, the Australes, contains species with small ray-pits, cones dehiscent at maturity and spring-shoots gradually changing, among the species, from a uninodal to a multinodal form. They are, without exception, species of the New World.
The third group, the Insignes, contains the serotinous species. The ray-pits are small and the spring-shoots are, with two exceptions, multinodal. With two exceptions, P. halepensis and P. pinaster, they are New World species.
These three groups, being the progressive sequence of a lineal evolution, are not absolutely circumscribed, but are more or less connected through a few intermediate species of each group. The systematic position of these intermediate species is determined by their obvious affinities. It cannot be expected that the variations, which take an important part in the evolution of the species, progress with equal step or in perfect correlation with each other.
As to specific determinations, a little experience in the field discloses an amount of variation in species that does not always appear in the descriptions of authors; and species that are under the closest scrutiny of botanists, foresters or horticulturalists, attest by their multiple synonymy their wide variation. The possibilities of variation are indefinite and, with adaptable Pines, the range of variation is somewhat proportionate to change of climate. In mountainous countries, where there are warm sheltered valleys with rich soil below cold barren ledges, the most variable Pines are found. The western species of North America, for instance, are much more variable than the eastern species, while in Mexico, a tropical country with snow-capped mountains, the variation is greatest.
Therefore in the limitation of species undue importance should not be given to characters responsive to environment, such as the dimensions of leaf or cone, the number of leaves in the fascicle, etc. Moreover, there are familiar examples (P. sylvestris, etc.) that show the possibility of wide differences in the cone of the same species.
In the following classification species only are considered without attempting to determine varietal or other subspecific forms. But varieties are often mentioned as one of the factors illustrating the scope of species. Synonymy serves a like purpose, but synonyms not conveying useful information are omitted, Roezl’s list of Mexican species, for instance, and variations in the orthography of specific names.
Pinus
1755 Pinus Duhamel, Traité des Arbres, ii. 121.
1790 Apinus Necker, Elem. Bot. iii. 269.
1852 Cembra Opiz, Seznam, 27.
1854 Strobus Opiz, Lotos, iv. 94.
1903 Caryopitys Small, Fl. Southeast. U. S. 29.
Leaves and shoots dimorphous, primary leaves on long shoots, secondary leaves on dwarf shoots. Flowers diclinous, the pistillate taking the place of long shoots, the staminate taking the place of dwarf shoots. Growth of wood and fruit emanating from the nodes; buds, branchlets and cones, therefore, in verticillate association. Leaves and staminate flowers in internodal position, the primary leaves along the whole length of the internode, subtending secondary leaf-fascicles on the apical, staminate flowers on the basal part. Buds compounded of minute buds in the axils of bud-scales, becoming the bracts of the spring-shoot. Branchlets of one or more internodes, each internode in three parts—a length without leaves, a length bearing leaves and a node of buds. Cone requiring two, rarely three years to mature, displaying its annual growths by distinct areas on each scale. Seeds wingless or winged, edible and nutritious.
The Pines are confined to the northern hemisphere, but grow in all climates and under all conditions of soil, temperature and humidity where trees can grow. Some of the species are of very restricted range, but others are adaptable and can cover wide areas. The sixty-six species are distributed as follows—
Eastern Hemisphere, 23.
1 exclusively African (Canary Islands).
2 exclusively European.
3 about the Mediterranean Basin.
2 common to Europe and northern Asia.
14 exclusively Asiatic.
Western Hemisphere, 43.
28 in western North America, of which 12 are confined to Mexico and Central America.
15 in eastern North America, of which 2 are exclusively West Indian.
The two sections of the genus correspond with those of Koehne (Deutsch. Dendrol. 28 [1893]) and his two names, Haploxylon and Diploxylon, are adopted here, together with his two subsections of Haploxylon, Cembra and Paracembra.
Of the two subsections of Diploxylon, Pinaster has been employed by Endlicher (Syn. Conif. 166 [1847]) and later authors for smaller or larger groups of Hard Pines. The subsection Parapinaster is now proposed.
The names of groups, Cembrae, Strobi, Cembroides, Gerardianae, Balfourianae, Pineae, Lariciones and Australes, are taken from Engelmann’s Revision of the Genus Pinus (Trans. Acad. Sci. St. Louis, iv. 175-178 [1880]). The remainder, Flexiles, Leiophyllae, Longifoliae, Insignes and Macrocarpae, are here proposed.
In order to bring the illustrations within the limits of the page the dimensions of cone and leaf, as shown on the plates, are a little smaller than life. In plates X and XXV the reproductions of the cones are reduced to 2/5 life-size.
Sections, Subsections, and Groups
| Bases of the fascicle-bracts non-decurrent | A—HAPLOXYLON |
| Umbo of the cone-scale terminal | a—Cembra |
| Seeds wingless. | |
| Cones indehiscent | I. Cembrae |
| Cones dehiscent | II. Flexiles |
| Seed with an adnate wing | III. Strobi |
| Umbo of the cone-scale dorsal | b—Paracembra |
| Seeds wingless | IV. Cembroides |
| Seed-wing short, ineffective | V. Gerardianae |
| Seed-wing long, effective | VI. Balfourianae |
| Bases of the fascicle-bracts decurrent | B—DIPLOXYLON |
| Fascicle-sheath or seed of Haploxylon | c—Parapinaster |
| Fascicle-sheath deciduous | VII. Leiophyllae |
| Fascicle-sheath persistent. | |
| Seed-wing of the Strobi | VIII. Longifoliae |
| Seed-wing of the Gerardianae | IX. Pineae |
| Fascicle-sheath persistent, seed-wing articulate, effective | d—Pinaster |
| Base of wing-blade thin or slightly thickened. | |
| Cones dehiscent at maturity. | |
| Pits of ray-cells large | X. Lariciones |
| Pits of ray-cells small | XI. Australes |
| Cones serotinous, pits of ray-cells small | XII. Insignes |
| Base of wing-blade very thick | XIII. Macrocarpae |