Cypress-pine, Ventenat 1808
Cupressaceae

Callitris - Cypress-pine description

Evergreen trees and shrubs. Bark fibrous, vertically furrowed, persisting and thickening with age. Densely, often irregularly branced from the base, with horizontal or gently ascending slender branches. Branchlets cylindrical or three-angled, branching three-dimensionally but with just one branch at a node. Without definite winter buds. Seedling and juvenile leaves in alternating quartets, crowded, sword-shaped, the free blades much longer than the attached leaf bases that run down onto the twig, standing straight out from the twig or at angles down to about 60°. Juvenile leaves usually relatively short-lived but recurring regularly on adult trees of some species, often giving way abruptly to adult foliage within a few successive attachments. Adult leaves in alternating trios (hence the scientific name, Latin for “beautiful threes”), scalelike, keeled or rounded, the free tips triangular, pressed forward against the branchlets, and tiny in comparison to the usually elongate attached leaf bases, giving the branchlets a jointed appearance.

Plants monoecious. Pollen cones numerous, single or clustered at or near the tips of the branchlets, oblong, with 3-10 alternating trios (rarely quartets) of pollen scales, each scale with two to six round pollen sacs. Pollen grains small (20-30 µm in diameter), spherical, minutely but conspicuously bumpy and with a tiny, obscure germination pore. Seed cones numerous, single or in clusters at the tips of short, stout branchlets, maturing in two seasons, then often persisting and remaining closed after maturity. Cones spherical to oval, with two alternating trios (or rarely quartets) of woody, triangular seed scales attached together at the base around a central, pyramidal or three-lobed column. Seed scales closing side to side, the inner trio usually longer than the outer one and touching at the tip of the cone. The scales with a variably expressed point below their tips, each outer scale with (none to) three to nine seeds in (none or) one to three rows, each inner scale with (2-)6-12 seeds in (one or) two to four rows, or fewer by abortion. Seeds oval and somewhat flattened, with (one or) two (or three) asymmetrical wings derived from the seed coat, the wings narrower to wider than the seed body and extending its whole length or beyond. Cotyledons two, each with one vein. Chromosome base number x = 11.

Wood unusually dense and hard, usually without pronounced heartwood colors, distinct growth rings, or resin canals, but often with distinctive, thin, microscopic bands across the bordered pits of the rounded tracheids.

Stomates lining the grooves between the attached leaf bases and sometimes also extending out onto the inner faces of the free tips at their bases. Each stomate sunken in a narrow pit beneath the four to six (or seven) subsidiary cells, which may be shared between adjacent stomates within and between rows and are topped by a high, steep, interrupted Florin ring. Leaf cross section with a single midvein bugging the twig side of the attached leaf bases and scarcely extending into the free tip. Midvein accompanied toward the outside by a single large resin canal and flanked by varying quantities of transfusion tissue. Photosynthetic tissue forming a prominent dense palisade inside the epidermis and hypodermis, giving way inward to a spongy mesophyll that includes patches of sclereids, often in inverse proportion to the amount of transfusion tissue. Seventeen species in Australia and New Caledonia.

The strong, durable, resistant wood of larger species of Callitris is highly prized for timber. A few species of the genus are in general cultivation in Australia, but elsewhere they are nearly restricted to botanical gardens and tree collections, primarily in Mediterranean climate regions. Cultivar selection has been minimal but a few foliage color variants are grown.

Callitris is the largest genus of Cupressaceae in the southern hemisphere. It is the characteristic conifer of dry forests and woodlands throughout Australia (though joined by its close relative Actinostrobus in the southwest), including the arid interior, where it is the only conifer. With their seed cones often remaining closed until scorched by fires, the Australian species are roughly equivalent ecologically to species of Cupressus in the northern hemisphere. The ecology in New Caledonia is rather different, the two species being found in both rain forests and dense shrublands, just like their close relative Neocallitropis.

Callitris is easily distinguished from Actinostrobus  by its lack of conspicuous rows of bracts at the base of the seed cone, the inequality of the two trios of seed scales, and the shorter free tips of the adult leaves. Neocallitropis never develops scalelike leaves and has narrower seed cones scales always in quartets. Natural hybridization occurs in only a few of the possible combinations of overlapping species. The fossil record of Callitris is quite sparse, as might be expected for a dryland genus, but it apparently extends back to the mid-Cretaceous.

References

• Farjon, A. (2010). A Handbook of the World's Conifers. Koninklijke Brill, Leiden.
• Eckenwalder, J.E. (2009) Conifers of the World: The Complete Reference. Timber Press, Portland.
• IUCN Red List of Threatened Species, International Union for Conservation of Nature and Natural Resources. Cambridge, UK /Gland, Switzerland

Copyright © Aljos Farjon, James E. Eckenwalder, IUCN, Conifers Garden. All rights reserved.