Southern pygmy pine, R. Philippi 1860
Podocarpaceae

Lepidothamnus - Southern pygmy pine description

Evergreen small trees and dwarf shrubs. Multistemmed or with a single, straight, often short, cylindrical to fluted trunk. Bark obscurely fibrous, thin, peeling in small irregular flakes. Crown open, upright or spreading with creeping to strongly upwardly angled branches. Branchlets all elongate, without distinction into short and long shoots, hairless, remaining green for several years, with conspicuous short grooves between the attached leaf bases, where visible. Resting buds poorly developed, consisting only of undeveloped ordinary foliage leaves. Leaves spirally attached, round or variably roundly triangular in cross section, needlelike and well separated in juveniles, scalelike and closely spaced in adults (hence the scientific name, Greek for “scaly shrub”), with a gradual transition between juvenile and adult foliage.

Plants monoecious or dioecious. Cones borne on shoots with adult, juvenile, or intermediate foliage. Pollen cones single at the tips of otherwise ordinary foliage shoots, cylindrical, without a distinct ring of bracts at the base and with 15-45 spirally arranged, roundly triangular pollen scales, each bearing two round pollen sacs. Pollen grains small to large (body 25-55 µm long, 50-100 µm overall), with two round, internally wrinkled air bladders. Bladders almost as large as or noticeably smaller than and partially tucked under (and around the longitudinal germination furrow of) the minutely bumpy, round to slightly oblong body. Seed cones single at the tips of otherwise ordinary foliage shoots, highly modified and reduced, with three to six closely spaced, spirally arranged bracts which become variably fleshy and may coalesce with each other and the axis into a berrylike podocarpium at maturity. Upper one (or two) bracts fertile, each bearing one upright seed surrounded at the base by a thin, cuplike seed scale and with a curled-over beak. Seeds maturing in two seasons. Cotyledons two, each with two veins. Chromosome base numbers x = 14, 15.

Wood, when present, hard and heavy, strong and durable, very resinous, with pale sapwood contrasting with the reddish yellow heartwood. Grain very fine and even, with evident growth rings marked by gradual narrowing of the latewood cells. Resin canals and individual longitudinal resin parenchyma cells both absent.

Stomates arranged in patches rather than distinct lines on both leaf surfaces. Each stomate deeply sunken beneath and largely hidden by the four to six inner subsidiary cells, which are surrounded by an outer circle of a comparable number of cells and are topped by a complete, roughly circular Florin ring. Midvein single, without a conspicuous surface midrib, with or without one resin canal directly beneath it, and with compact bands of transfusion tissue on either side. Photosynthetic tissue on both surfaces.

 Three species in New Zealand and in southern South America. This small genus contains two of the smallest living conifer species in the world, and the third is no forest giant. At least two also have among the smallest genomes (quantities of DNA in their chromosomes) known for conifers. The two smaller species, as two of the naturally most dwarf extant conifers, make interesting subjects for bog gardens in wet, mild temperate regions, but they are scarcely in cultivation and there has been no cultivar selection in the genus.

The species of Lepidothamnus are generally similar in appearance to species of several other small podocarp genera of New Zealand and Australia: Halocarpus, Lagarostrobos, and Manoao. DNA studies yield varied results but generally show that it is loosely associated with these genera. Although it is not as closely related to these genera as they are to each other, it is still much more closely related to them than it is to the species of Dacrydium, the genus in which all of these species were generally included before 1982. In that year, Quinn segregated these small genera from Dacrydium (or reinstated in the case of Lepidothamnus, which had been formally described and named in 1861 but which had quickly fallen out of use). They differ from Dacrydium, and from each other, in many features of seed cones, epidermal structure, embryo development, wood anatomy, chromosome arrangements, and chemistry of their oils and pigments. All these features had been described previously but had only been considered indications of variation within Dacrydium. As it turned out, however, these differences reflect a much deeper division among all the species once included in Dacrydium, separating Lepidothamnus and its relatives into a different fundamental grouping of genera within the family than the one including Dacrydium as presently understood.

One of the distinctive characteristics of Lepidothamnus is the hooked beak of the seed (the micropyle), through which pollen enters the immature ovule during pollination and fertilization. With this structure, the ovules of Lepidothamnus preserve the hanging pollination droplet typical of the podocarps, even though they are upright rather than being pointed down into the cone axis as they are in the majority of podocarp species. Thus the pollen grains, with their air bladders, can still float up into the micropyle even though the ovules are reoriented compared to other podocarps.

The known fossil record of Lepidothamnus is very sparse but dates back to the late Eocene in Tasmania, more than 35 million years ago. These fossils are most similar to the largest extant species, Yellow silver pine (Lepidothamnus intermedius) of New Zealand, and the genus is no longer present in Australia today.  

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.