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Sickle pine, de Laubenfels  1969


Evergreen trees and shrubs, of varying habit from prostrate to upright, occasionally reaching the canopy, often with multiple stems. Bark fibrous, smooth, flaking in small patches. Crown conical to narrowly to very broadly and shallowly dome-shaped. Vegetative branchlets all elongate, without distinction into long and short shoots, hairless, remaining green for a least the first year, grooved between the elongate, attached leaf bases. Resting buds inconspicuous and unspecialized, consisting of loosely arranged scale leaves that persist at the base of new growth. Leaves spirally attached to the twigs, of three main forms with some transitional leaves. Seedling leaves radiating all around the twigs, flattened top to bottom, narrowly sword-shaped, with stomatal bands on either side of the prominent midrib beneath. Scale leaves of adults radiating all around the twigs, confined primarily to reproductive shoots and to the bases of growth increments. Juvenile and adult needlelike foliage leaves flattened into two rows by the flexure of the blade near its base. Each leaf flattened side to side (and thus with a left and right side rather than a top and bottom side), somewhat sickle-shaped (hence the scientific name, Latin for “sickle leaf”), the base curved down toward the base of the twig and the tip curved forward toward its tip.

Plants dioecious. Pollen cones cylindrical, single or in clusters of two to four at the ends of short, scaly stalks in leaf axils or (less frequently) at the ends of shoots. Without a conspicuous circle of distinctive bracts at the base and with numerous, densely spirally arranged pollen scales, each bearing two pollen sacs. Pollen grains medium (body 30-35 µm long, 60-70 µm overall), with two round air bladders that extend along the sides as well as out from the ends of the body so that, from above, the body appears to be surrounded by a single, large, elliptical sac. Surface coarsely sculptured with squiggly lines except over the top of the body, which is finely dotted. Seed cones single at the ends of short scaly stalks in the axils of foliage leaves or (less frequently) at the ends of shoots, these stalks curling back at maturity, maturing and falling in a single season. Cones highly modified and reduced, the reproductive part with 8-12 bracts that unite with the cone axis at maturity to form a red, swollen, juicy podocarpium bristling with the conspicuous free tips of the bracts. Seeds single, egg-shaped  but slightly flattened and unwinged, embedded at the base in each of one (or two) humped seed scales (the epimatium). Hump becoming more prominent during maturation as the opening of the ovule is reoriented away from the base and the mature seed finally points away at an angle from the cone axis. Seed with a pair of ridges uniting over the tip. Cotyledons two, each with two veins. Chromosome base number x = 10.

Wood soft, light, fragrant, light brown, with little differentiation between sapwood and heartwood. Grain fine and even, with indistinct growth rings. Resin canals absent but with individual resin cells and abundant nonresinous wood parenchyma.

Stomates in numerous lines of varying lengths and degrees of continuity on both surfaces. Each stomate partially tucked underneath the four to six surrounding subsidiary cells, which are often shared between adjacent stomates in a row, and which may or may not be (even on a single leaf) topped by a Florin ring. Leaf cross section with a single, prominent or obscure midvein narrowly raised as a midrib on both sides, accompanied beneath (seemingly the outer side of the midvein) by a single large resin canal, flanked by wedges of transfusion tissue, and with scattered accessory transfusion tissue extending throughout the center of the leaf. Photosynthetic tissue with a palisade layer covering both sides of the leaf inside the epidermis and its associated incomplete hypodermis, leaving little room for spongy mesophyll.

Six species in northern Malesia, from central Malaya (Malaysia) and southern Luzon (Philippines) to eastern New Guinea (Papua New Guinea) and in New Caledonia.

Although it was the first of the several new genera whose separation from Dacrydium since 1969 has generally been accepted by most taxonomists, Falcatifolium is actually much more closely related to the species of Dacrydium in the restricted sense now generally adopted than are the genera segregated more recently. While they were separated from Dacrydium more than 10 years after the separation of Falcatifolium, DNA studies show that Halocarpus, Lagarostrobos, Lepidothamnus, and Manoao are only distantly related to Dacrydium while Falcatifolium is its closest relative. Falcatifolium was long recognized as a distinctive group within Dacrydium before its generic segregations, even though it was never given formal botanical status as a section or subgenus. It is distinguished from Dacrydium by the position of the cones, the form of the epimatium, and the distinctive form of the leaves.

The more or less sickle-shaped leaves flattened side to side rather than top to bottom are highly unusual in conifers, and the only other extant genera with full-blown development of this leaf form are also podocarps, Acmopyle and juvenile foliage of Dacrycarpus (some species of Picea are somewhat diamond-shaped in cross section but have little or no vertical blade development). Because of the particular evolutionary relationships of these three genera to each other, to Dacrydium, and to Podocarpus and its closest relatives, it is not clear whether this leaf form was inherited from a common ancestor or evolved independently more than once.

The living species of Falcatifolium are very closely related and homogeneous, differing primarily in the size, proportion, and detailed shape of the foliage leaves. The genus is not in general cultivation, and there has been no cultivar selection. The fossil record is very sparse, but there are confirmed occurrences in the mid-Eocene of southeastern Australia, some 45 million years ago, so the separation from the other genera must be older than that. The same sediments, and slightly more recent Oligocene sediments in Tasmania, contain shoots of an extinct genus, Sigmaphyllum, with leaves of the same form, but a distinct epidermal structure from that of Falcatifolium species.





Attribution from: Conifers Garden