Phyllocladus alpinus (mountain toatoa) description

Conservation Status

Phyllocladus alpinus

Hooker (1853)

Common names

Mountain toatoa (Silba 1986).

Taxonomic notes

Type: New Zealand, South Island, Nelson, J. C. Bidwill 137 (lectotype K). Syn: P. aspleniifolius var. alpinus (Hook.f.) H.Keng, P. trichomanoides var. alpina Parl.

Hooker (1853) gave this taxon species rank and kicked off the taxonomic debate when he wrote "I have very many specimens of this plant from Mr. Bidwill and Mr. Colenso, and fear it may prove only an alpine variety of P. trichomanoides. Mr. Bidwill, however, thinks the contrary, judging from habit and appearance." Parlatore (1868) evidently agreed with Hooker; he made it a variety of P. trichomanoides. Keng (1978) moved it over to P. aspleniifolius because he distinguished the species of Phyllocladus mainly on whether the phylloclades are simple or pinnate, which Farjon (2010) thought a weak argument; he moved it back based on morphology and biogeography (both P. trichomanoides and P. alpinus are endemic to New Zealand). Recent morphological analyses (Khan et al. 2022, 2023) have aligned P. alpinus with P. hypophyllus of New Guinea, but this is biogeographically implausible and the authors do not address the question of whether this similarity has a phylogenetic explanation. Wagstaff (2004) appears to be the only molecular study of the genus, finding that nuclear DNA (ITS sequences) clearly discriminate the taxa and place P. alpinus sister to P. trichomanoides. Besides this, various authors have noted that there seems to be significant morphological variation within P. alpinus, with at least two distinct ecotypes, though they have not been formally described (Wardle 1969, Wagstaff 2004). Based on this information, it is at the least a subspecies of P. trichomanoides, but has not been so described, and so I am conservatively treating it at species rank.

Description

Monoecious, strongly aromatic shrub or tree up to 9 m tall, trunk short, up to 40 cm in diameter. True leaves occur only on seedlings and occasionally on young plants. They are narrow-linear, acute, deciduous, up to 1.5 cm long, on older plants shorter. Phylloclades alternate to subopposite, rhachis short. Phylloclades of juvenile plants up to 2 cm long, deeply divided, thin, with narrow-linear segments, glaucous below; of adults thick, coriaceous, 1-2.5 cm, occasionally up to 6 cm long, 2 cm wide. Phylloclade shape various; narrow-rhomboid or spathulate, sparingly or much lobed, often elliptic to obovate, cuneate at base, apex subacute to broad-obtuse, margins crenate, leaf-denticles small. Pollen cones 5-6 mm long in fascicles of 2-5, rarely solitary, apical, with pedicels 1-2 mm long; sporophylls with small variously shaped apiculi, stems erose. Female cones arise along the margins or on the stalks of the phylloclades; receptacle of red, fleshy scales; mature heads ca. 6-7 mm diameter. Seeds nutlike, black, exserted, ovoid, compressed, ca. 2.5 mm long, obtuse; cupule white, irregularly lobed, up to 2/3 length of seed (Allan 1961, Salmon 1996).

Distribution and Ecology

New Zealand: N and S Islands from latitude 36° 50' southwards. It is found on the Coromandel Peninsula between Cape Colville and Te Aroha and from the volcanic plateau southwards between 900 m and 1,600 m to Mt Cargill, Fiordland and Southland. In South Westland and Southland it occurs down to sea level (Allan 1961, Salmon 1996). Based on data from 1119 collection localities, its climate preferences include a mean annual temperature of 8.7°C, with an average minimum in the coldest month of -0.7°C, and a mean annual precipitation of 2705 mm (Biffin et al. 2011, Table S5). Hardy to Zone 8 (cold hardiness limit between -12.1°C and -6.7°C) (Bannister and Neuner 2001).

It occurs in subalpine and scrub forest; also lowland forest in west of S Island. The wood is elastic, making the plant very wind-resistant (Allan 1961, Salmon 1996).

Remarkable Specimens

No particularly large or tall specimens are recorded. An indication of potential ages comes from one tree-ring chronology, presumably based on living tree material, covering 259 years (data on file with ITRDB).

Ethnobotany

See Conifers of New Zealand for a review of the historic role of forests in native and European cultures of New Zealand. However, there is not much evidence that this small, mostly subalpine tree was extensively used or affected by humans.

The species has proven useful in dendrochronology. Development of tree-ring chronologies apparently began with a collection in the 1970s at Pegleg Creek (S Island: 42°S, 171°E; 279 years) by Dunwiddie (1979). P. alpinus tree ring data have been used in a study of climate change in New Zealand over the last thousand years (Burrows and Greenland 1979). A survey of dendrochronological work with the species is provided by Norton and Palmer (1992).

Observations

This species is very common in the alpine and subalpine shrublands and adjacent montane forests of Tongariro National Park. It can be seen from the north trailhead up to Ketetahi Hut on the Tongariro Crossing, and on all of the walks along the Bruce Road and around Whakapapa Village on Mount Ruapehu. It is probably found on most other subalpine scrub trails in the Ruapehu area as well. The walk up to Ketetahi Hut is particularly interesting because the mountain toatoa grows as a forest tree up to about 9 m tall beneath taller trees (including Podocarpus laetus) near the start of the walk, and diminishes in stature as the track climbs upward until it is only a battered shrub growing in the company of Podocarpus nivalis and Lepidothamnus laxifolius.

Remarks

The epithet alpinus refers to the species' mostly-subalpine distribution.

Citations

Allan, H. H. 1961. Flora of New Zealand. Volume I, Indigenous Tracheophyta. Wellington: R.E. Owen Government Printer.

Hooker, J. D. 1853. Botany of the Antarctic Voyage, V.2. Flora Novae Zelandiae, p. 235. Available: Biodiversity Heritage Library, accessed 2025.02.22.

Keng, H. 1978. The genus Phyllocladus (Phyllocladaceae). Journal of the Arnold Arboretum 59:249–273.

Khan, R., Hill, R. S., Dörken, V. M., and Biffin, E. 2022. Detailed seed cone morpho-anatomy of the Prumnopityoid clade: An insight into the origin and evolution of Podocarpaceae seed cones. Annals of Botany 130(5):637–655. https://doi.org/10.1093/aob/mcac097.

Khan, R., Hill, R. S., Liu, J., and Biffin, E. 2023. Diversity, distribution, systematics and conservation status of Podocarpaceae. Plants 12(5):1171. https://doi.org/10.3390/plants12051171.

Parlatore, F. 1868. P. 498 in de Candolle, A. P. (ed.), Prodromus Systematis Naturalis Regni Vegetabilis 16(2). Available: Biodiversity Heritage Library, accessed 2025.02.22.

Wagstaff, Steven J. 2004. Evolution and biogeography of the austral genus Phyllocladus (Podocarpaceae). Journal of Biogeography 31:1569-1577.

Wardle, P. 1969. Biological flora of New Zealand. 4. Phyllocladus alpinus Hook.f. (Podocarpaceae) mountain toatoa, celery pine. New Zealand Journal of Botany 7:76–95.