Podocarpus decumbens () description

Podocarpus decumbens

N.E. Gray 1955

Common names

Taxonomic notes

Gray (1955) placed P. decumbens into section Eupodocarpus, subsection F, along with P. longifoliolatus of New Caledonia and P. decipiens of Fiji, a grouping based on leaf resin canal position. The molecular analysis by Knopf et al. (2011), discussed in the "Taxonomic notes" for Podocarpus, places the New Caledonia species into a single clade. That analysis did not consider P. decumbens, but it did consider the very similar P. longifoliolatus; although that species is sister to the remainder of the clade, it is still realistic from morphological, molecular and biogeographic perspectives to place P. decumbens amongst a clade of New Caledonian Podocarpus. Due to its unusual growth habit and ecological setting, adapted to open montane areas with ultramafic soils on an oceanic tropical island, it is likely a relatively recently-evolved species within the clade.

Description

Decumbent shrubs, sometimes semi-erect but not more than 40 cm tall, rooting from the stems, spreading over rocks or other shrubs (but without specialized structures for grasping other plants, thus not lianoid), often forming extensive colonies through layering. Bark thin, exfoliating with fibrous strips; outer bark yellow-brown and inner bark red-brown. Foliage branches round, finely striated; terminal buds ca. 4 mm long with erect, lanceolate outer scales to 10 mm long (inner scales much shorter). Leaves mostly in tufts towards ends of twigs, coriaceous, light green on both surfaces, linear, widest above the middle part, 4.5-8 cm × 6-9 mm, gradually tapering to a petiolate base; margins revolute, straight; apex narrowing abruptly, usually obtuse. Midrib prominent, acute or obtuse on adaxial (upper) side, flattened on abaxial side. Stomata in numerous intermittent lines forming bands on either side of abaxial midrib. Pollen cones axillary, solitary, sessile, subtended by triangular, keeled bud scales, elongating to 15-30 × 3-3.5 mm; microsporophylls spirally arranged, triangular, bearing two sub-basal pollen sacs. Seed cones axillary, solitary on a 5-7 mm long peduncle; receptacles subtended by two 3-4 mm long, linear bracts composed of an axis with 3-4 fused bracts with exserted tips, one of which is fertile, all swelling to an 8-10 cm long, red and succulent body. Seeds solitary, including the epimatium 6-7 x 4 mm (probably growing slightly larger but no completely mature seeds are known), with a small crest. Apart from growth habit, this species resembles P. longifoliolatus, but only single-seeded cones (receptacles) have been reported (Farjon 2010).

The type description (Gray 1955) includes these observations: "The description of Podocarpus decumbens was written from the specimen collected by Luc Chevalier on Dec. 1, 1949 ... The very low creeping habit is rare in this genus of trees but it is interesting to note that Podocarpus gnidioides, in subsection D, of similar habit and only a little larger, is also found on Montagne des Sources. There is no confusing these species in the field or herbarium as the foliage is very different, the leaves of Podocarpus gnidioides being only up to 2 cm. long and 2 mm. broad. Only the sketch made by M. Chevalier convinces me that the twig with such large leaves, up to 5.8 cm. long and 7 mm. wide, came from so small a mature plant."

Distribution and Ecology

New Caledonia (de Laubenfels 1972), where known from only three sites in the southern island, in Montagne des Sources and on Mt Kouakoué. It grows in maquis (a shrub vegetation type) at 800 to 1,000 m elevations on ultramafic substrates, in areas with high precipitation distributed throughout the year (Thomas 2009).

This map shows herbarium records of Podocarpus species native to New Caledonia. Red is P. decumbens, dark green is P. gnidioides, orange is P. longifolioliatus, yellow is P. lucienii, purple is P. novae-caledoniae, green is P. polyspermus, and blue is P. sylvestris. Click on an icon for further information. Distribution data from GBIF (2020.03.30), edited to remove duplicates.

"The rarest podocarps [in New Caledonia] undoubtedly formerly occupied much larger areas but are now restricted to sites in wet montane forest on ridges (Podocarpus decumbens, critically endangered, and P. longifolioliatus, endangered) or along the margins of watercourses (Dacrydium guillauminii, Retrophyllum minus), which have provided them with a refuge from fire" (Turner and Cernusak 2011). This species faces an extremely high risk of extinction in the wild due to an extremely limited distribution (known only from 3 sites with a total area of 8 km²). "Although all three sites are relatively inaccessible and within protected areas, they remain vulnerable to fires. The three subpopulations are regarded as severely fragmented due to their geographic and ecological isolation. In Montagne des Sources, recent fires have come close to destroying one subpopulation" (Thomas 2009).

Remarkable Specimens

Ethnobotany

No uses are known. The unusual habitat could make it an object of interest for horticulture in areas of suitable climate (probably Zone 9 or warmer), but a 2020 search found only a single occurrence outside New Caledonia--in the collection of the Royal Botanic Garden Edinburgh.

Observations

Remarks

The epithet is a common one, referring to prostrate plants that lie upon the ground, with only the growing tip erect.

Citations

Gray, Netta E. 1955. A taxonomic revision of Podocarpus IX. The South Pacific species of Section Eupodocarpus, subsection F. Journal of the Arnold Arboretum 36:199-206 (p. 202). Available: Biodiversity Heritage Library, accessed 2020.03.30.

Thomas, P. 2009. Podocarpus decumbens. In: IUCN 2010. IUCN Red List of Threatened Species. Version 2010.3. www.iucnredlist.org, accessed 2010.10.07.

Turner, B. L., and L. A. Cernusak. 2011. Ecology of the Podocarpaceae in Tropical Forests. Washington, DC: Smithsonian Institution Scholarly Press.