Retrophyllum filicifolium

(N.E. Gray) R.R. Mill 2016

Common names

Lehil (New Britain), moegò (New Guinea – Wissel Lakes, Kapaukoe language) (Mill 2016).

Taxonomic notes

Syn: Podocarpus filicifolius Gray 1962 (Mill 2016). This species was long considered synonymous with Retrophyllum vitiense, until Mill (2016), in his fine monograph on Retrophyllum, identified multiple and consistent morphological differences between the two taxa, and showed that they have separate and disjunct distributions; thus they are appropriately distinguished at specific rank.

Description

Trees to 60 m tall and 130 cm dbh, sometimes spur-buttressed at base, typically with a single trunk and a compact crown. Bark first smooth, light or medium brown, with age becoming flaky, fissured, dark brown or blackish; inner bark reddish-brown, salmon or pink; wood pale orange, yellow or white. Terminal buds on primary branches globose or ovoid; bud scales present in 4 series, the lowest pair longer and wider than the others, all ovate or ovate-rhombic and slightly keeled, acute, brownish with narrow pale margin, shed early leaving cream-colored transversely narrowly rhombic scars much paler than the branchlet; buds on foliage shoots usually remaining dormant, ovoid. Ultimate juvenile shoots 65–210 mm, usually with 11–20 pairs of foliage leaves. Juvenile foliage leaves 4–7 mm apart, heterofacially turned at base, diverging at 60–85°, shortly petiolate, leaf blade lanceolate or narrowly lanceolate, leaves near middle of shoot 18–40 × 4.2–6 mm, the apex often indistinctly mucronate. Adult (and juvenile) trees with dimorphic shoots, most shoots bearing foliage shoots but leaders bearing scale leaves; shoot flattening heterofacial with the decurrent bases running straight down the internodes. Ultimate adult foliage shoots 20–90 mm long with 4–18 pairs of leaves spaced 2–7 mm apart. Adult leaves heterofacially twisted, subsessile, leaf blades diverging at 50–80°, mid to deep green, narrowly elliptic to elliptic or oblong, widest just below the middle), those near middle of shoot 7–25 × 3–5 mm, coriaceous, margin narrowly hyaline, amphistomatic. Pollen cones terminal on lateral shoots arising just above bud scales of previous season, subtended by a bract, 1–several, ellipsoid or ovoid; microsporophylls 20–32 per cone, in 5–8 whorls; microsporangia reniform. Female cones borne laterally from near the base of an ultimate foliage shoot of the previous year's growth, the reproductive shoot subtended by a bract. Peduncle 5–10 mm, equalling or shorter than unripe cone and always shorter than ripe cone, erect when young, becoming pendulous, with 3–5 pairs of bracts below the cone axis. Peduncle bracts ovate to ovate-rhombic, c. 1.5 × 0.3–0.5 mm, with narrow scarious margins. Cone axis formed of c. 4 sterile bracts and 1 or 2 fertile bracts. Sterile bracts ephemeral, elliptic, larger than peduncle bracts, at first spreading but soon becoming deflexed and falling. Receptacle obovoid, purplish-brown, glaucous. Fertile bract initially erect, its proximal half fused to the epimatium and lacking a keel. Cones obovoid or pyriform, c. 26 × 17 mm; epimatium green when young becoming red when ripe, glaucous when unripe, not crested, with conical, slightly hooked beak at micropylar end (Mill 2016).

The following characters serve to separate R. filicifolium from R. vitiense (Mill 2016):

• Pollen cones have fewer microsporophylls (typically 20–32 in 5–8 whorls as opposed to 44–80 in 11–20 whorls). Terminal pollen cones sometimes occur in R. vitiense, but not in R. filicifolium.
• Young female cones have fewer sterile bracts on the female cone axis (about 4, not 6–8) that soon fall, not persisting till the cones reach resting phase.
• The proximal half of the fertile bract lacks a keel, and the receptacle is obovoid rather than cylindrical.
• The ripe seed cones are slightly larger, c. 26 × 17 mm rather than 15–23 × 10–12 mm.
• Bud scales are shed sooner and leave pale scars on the branchlet.
• Juvenile and adult ultimate foliage shoots are shorter, with fewer pairs of leaves, although there is overlap between the species in this character.
• The broadest point of both adult and juvenile leaves is near the middle rather than towards the base.

Distribution and Ecology

Indonesia and Papua New Guinea: Morotai (the type locality), New Guinea, New Ireland, and New Britain; at elevations of (300-)900-1500 m, significantly higher than R. vitiense. R. filicifolium grows in tall primary montane rain forest or ridge forest, often associated with Dacrycarpus spp. (most likely D. imbricatus var. robustus), emergent palms such as Gulubia and other trees including Agathis labillardieri, Podocarpus, Serianthes, Syzygium, Casuarina rumphiana, and sometimes in shade among bamboos (Mill 2016).

Distribution, redrawn from Figure 4 in Mill (2016).

The IUCN has not recognized this as a species distinct from R. vitiense and their conservation assessment for that species conflates the two taxa. However, it is still probably accurate to assess R. filicifolius as "least concern" under IUCN criteria due to its extensive distribution within New Guinea (Mill 2016).

Remarkable Specimens

Although I have seen no data for individual trees, the potential sizes listed by Mill (2016), 60 m tall and 130 cm dbh, would rank this as the tallest and nearly the largest species in Retrophyllum.

Ethnobotany

No recorded use, but like R. vitiense, it is likely exploited for its timber, which is of high quality.

Observations

No data as of 2023.02.22.

Remarks

Gray (1962) explained that the epithet filicifolium "refers to the fern-like appearance of the pinnately leaved twigs, reminiscent of the royal fern, Osmunda regalis”.

Citations

Gray, N. E. 1962. A taxonomic revision of Podocarpus XIII. Section Polypodiopsis in the South Pacific. Journal of the Arnold Arboretum 43: 67–79.

See also