Sandplain cypress, Miquel 1845
Cupressaceae

Actinostrobus - Sandplain cypress description

Evergreen shrubs or small trees with fibrous furrowed bark peeling in thin flakes and strips. Densely branched from the base with stiff horizontal or ascending branches to form an irregularly conical crown. Branchlets cylindrical or three-angled, branching three-dimensionally. Without specialized resting buds. Seedling leaves in alternating quartets at first, followed by alternating trios, needlelike, well separated on the twig by the long leaf bases running down onto it and standing out from it at an angle of about 60°, the free tips progressively shorter in juvenile and adult foliage. Adult leaves in alternating trios, scalelike, keeled, with elongate leaf bases running down on the twigs and prominent, triangular free tips with thickened margins angling outward to give a slightly bristly texture to the foliage.

Plants monoecious. Pollen cones numerous, single at the tips of short lateral branchlets, oblong, with five to seven alternating trios of pollen scales, each scale with two to four pollen sacs. Pollen grains small (25-35 µm in diameter), spherical, minutely but conspicuously bumpy, without a germination pore. Seed cones numerous, single at the tips of short lateral branches close to the trunk, maturing in a single season but remaining closed on the tree after maturity. Cones spherical to oval at maturity, apparently with a single whorl of six triangular fertile seed scales attached at the base around a central column and closing side to side so that tips of all six meet at the top, actually of two alternating trios, one with slightly wider scales than the other. Fertile scales each with one to three sterile scales beneath grading into the foliage leaves of the branchlet and with one or two seeds. Seeds oval, with (two or) three unequal to nearly equal triangular wings derived from the seed and extending along the whole length of the seed body or beyond. Cotyledons two, each with one vein. Chromosome base number x = 11.

Wood odorless, soft, light, with pale sapwood weakly contrasting with the small core of slightly darker heartwood. Grain somewhat uneven and moderately fine, with poorly defined growth rings marked by one or two rows of smaller latewood tracheids with wall thickness similar to that of those in earlywood. Resin canals absent but sometimes with traumatic resin pockets and with fairly numerous, scattered individual resin parenchyma cells often more concentrated near the ring boundaries and thus helping to delimit them.

Stomates in a single narrow band on either side of the midline both above and beneath. Each stomate deeply sunken beneath the four or five (to six) surrounding subsidiary cells, which are topped by a steep-sided Florin ring inside an encircling channel. Leaf cross section with a single midvein linked also by transfusion tissue to the branchlet core. Outer (lower) face of leaf with a thin layer of hypodermis inside the epidermis adjacent to the palisade photosynthetic tissue, which lies outside a very open spongy mesophyll accompanied by resin cavities.

Three species in southwestern Australia. Actinostrobus is closely related to Callitris, as long recognized by their morphology and ecology and now seen also in their DNA sequences. Both genera inhabit the dry forests and woodlands of Australia, corresponding ecologically to the more distantly related Widdringtonia in southern Africa and Cupressus, Juniperus, and Tetraclinis in northern Africa and elsewhere in the northern hemisphere. The two genera also share leaves in trios with conspicuous elongate leaf bases, giving a jointed appearance to the branchlets. Actinostrobus, however, has longer free leaf tips than Callitris, leading to a slight bristliness. The seed cones of both genera have an apparent whorl of six triangular fertile scales, but the outer trio in Callitris is much smaller than the inner trio, and their tips do not reach to the tip of the cones, unlike the nearly equal, colorful trios of Actinostrobus (named from the Greek for “star cone”). The scales of Callitris usually have more than one or two seeds and do not have neat rows of sterile scales beneath them. The shrubs are too small to be of much economic significance for wood products. Grown to a limited extent in botanical gardens and Australian home gardens, there has been no cultivar selection in this genus. There is no known fossil record for Actinostrobus, which is not surprising given the dryland habitats of the species.

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.