Pseudopanax

Houpara Pseudopanax lessonii, from Kahuroa.

Belongs within: Araliaceae.

Five-fingers and lancewoods
Published 18 January 2020

Longtime readers of this blog will know that my knowledge of plants has always been fairly rudimentary. As a young’un, I only ever learnt to distinguish some of the more common and visible varieties. As a student, I did take a few botany classes, but only really enough to learn that plant biology is complicated and terrifying. Since then, I’ve continued in much the same vein. But for today’s post, I’m looking at something I do recall being aware of in my youth: the lancewoods and five-fingers of the genus Pseudopanax.

Horticultural variant of coastal five-finger Pseudopanax lessonii, copyright Leonora Enking.

Pseudopanax is a genus of a dozen species of small tree (mostly growing about five to seven metres in height) found only in New Zealand (Perrie & Shepherd 2009). Various species have also been assigned to the genus from locations around the Pacific (China, Tasmania, New Caledonia and Chile) but recent studies have lead to their exclusion. A handful of New Zealand species previously included in Pseudopanax have also been separated as the genus Raukaua (Mitchell et al. 1997). The historical taxonomy of the group is confusing, with species being variously attributed to genera Panax, Nothopanax, Neopanax and Polyscias. Things seem to have settled down a bit in recent years but there is still the possibility we may one day see Neopanax rise again (Perrie & Shepherd 2009).

Chatham Islands lancewood Pseudopanax chathamicus, copyright Krzysztof Ziarnek, Kenraiz.

Pseudopanax belongs to the family Araliaceae, a group that is primarily composed of tropical and subtropical shrubs and trees. Araliaceae are commonly referred to as “the ivy family”, after one of their best-known members, the common ivy Hedera helix, but, as is not uncommon when a tropical family gets named after one of their European outliers, ivy is pretty weird by Araliaceae standards. Pseudopanax species are perhaps a bit more typical. They have large leaves, often more or less toothed or lobed along the margins. In a number of species, the leaves are palmately divided into three or five separate leaflets, hence the aforementioned vernacular name of ‘five-finger’. In one group of species, the lancewoods, the lateral leaflets have been lost and the now undivided leaf is more or less long and narrow. Hybrids between five-fingers and lancewoods may have multiple leaflets like a five-finger but the leaflets shaped like those of a lancewood; New Zealand botanist Leon Perrie has written a post about hybridisation in this genus that you can read here. The trees are usually dioecious (male and female flowers are borne on separate trees) and the individually small flowers are borne aggregated in compound umbels. Fruits are fleshy berries.

Collection of lancewoods Pseudopanax crassifolius showing the variation in leaf form, copyright Petra Gloyn. Two individuals on the left are young tress with hanging leaves; to the right is a more mature individual with spreading leaves.

Within Pseudopanax, the lancewoods are particularly renowned for their exhibition of heteroblasty, a phenomenon where the appearance of the leaves changes significantly as the tree matures. Juvenile leaves of the common lancewood P. crassifolius and toothed lancewood P. ferox are remarkably long, slender, strongly toothed along the margin, stiff and leathery, and hang downwards around the young tree like a skirt. As the tree approaches its mature height, it starts producing shorter, softer, less serrate leaves that are held in a more or less horizontal position.

Changes in growth habit with maturity seem to be surprisingly common among New Zealand plants and there has been a lot of discussion about why this might be. One suggestion that has certainly received a lot of public attention is that it is a relic of browsing by the large herbivorous birds such as moa that dominated the New Zealand environment prior to human settlement. Juvenile plants developed a habit that was energetically expensive but discouraged browsing by birds; as they grew high enough to escape the reach of such browsers, they changed to a less demanding form. I personally tend to be skeptical of these kinds of claims of historical baggage, not least because the extinction of one-half of the equation makes them very hard to test in any way, but I will admit that this case does perhaps have a bit more credibility than, for instance, claims elsewhere of giant fruits being dependent on long-extinct megafauna. Alternatively, it has been suggested that changes in growth habit may be related to climatic conditions; the juvenile leaves of P. crassifolius dissipate heat more effectively than those of mature trees (Gould 1993). Heteroblasty is less pronounced in the montane lancewood P. linearis of the South Island and almost absent in the Chatham Islands lancewood P. chathamicus, an insular derivative of P. crassifolius. Were these species insulated from the selective pressures affecting the other two? It should also be pointed out that the two proposals mentioned here are not mutually exclusive; the consideration of one as a factor does not automatically rule out the other.

Systematics of Pseudopanax
<==Pseudopanax Koch 1859 [incl. Neopanax Allan 1961]A61
|--P. arboreusDK-DW00 (see below for synonymy)
|--P. chathamicum Kirk 1899A61
|--‘Panax’ colensoi Hooker 1853 [=Neopanax colensoi (Hooker) Allan 1961, Nothopanax colensoi (Hooker) Seem. 1866]A61
| |--P. c. var. colensoiA61
| `--P. c. var. montanum Kirk 1899 [=Neopanax colensoi var. montanum (Kirk) Allan 1961]A61
|--P. crassifolium (Sol. ex Cunn.) Koch in Koch & Fint. 1859 (see below for synonymy)A61
|--P. discolor (Kirk) Harms 1894 [=Panax discolor Kirk 1871]A61
|--P. ferox Kirk 1889 [=Panax ferox Kirk 1878]A61
|--P. gilliesii Kirk 1899A61 [incl. Panax lessonii var. heterophylla Kirk 1878A61, Aralia heterophyllaC06]
|--‘Nothopanax’ kermadecensis Oliver 1926 [=Neopanax kermadecense (Oliver) Allan 1961]A61
|--P. laetevirensD03
|--‘Neopanax’ laetum (Kirk) Allan 1961 [=Panax arboreum var. laetum Kirk 1899, Nothopanax laetum (Kirk) Cheesem. 1923]A61
|--P. lessonii (DC.) Koch in Koch & Fint. 1859A61 (see below for synonymy)
|--P. lineare (Hooker) Koch in Koch & Fint. 1859 [=Panax linearis Hooker 1853, Nothopanax lineare (Hooker) Harms 1894]A61
`--‘Nothopanax’ × macintyrei Cheeseman 1925 [Neopanax arboreum × Ne. simplex]A61

Pseudopanax arboreusDK-DW00 [=Panax arboreum Murr. 1774A61, *Neopanax arboreum (Murr.) Allan 1961B88, A61, Nothopanax arboreum (Forster) Seem. 1866A61]

Pseudopanax crassifolium (Sol. ex Cunn.) Koch in Koch & Fint. 1859 [=Aralia crassifolia Sol. ex Cunn. 1839, Hedera crassifolia Gray 1854, Panax crassifolium (Sol.) Decne & Planch. 1854; incl. Pa. coriaceum Regel 1859, Pa. longissimum Hooker 1864, Pseudopanax crassifolium var. trifoliolatum Kirk 1889, P. crassifolium var. unifoliolatum Kirk 1889]A61

Pseudopanax lessonii (DC.) Koch in Koch & Fint. 1859A61 [=Panax lessonii DC. 1830A61, Aralia lessoniiC06, Cussonia lessonii Rich. 1832A61, Hedera lessonii Gray 1854A61]

*Type species of generic name indicated

References

[A61] Allan, H. H. 1961. Flora of New Zealand vol. 1. Indigenous Tracheophyta: Psilopsida, Lycopsida, Filicopsida, Gymnospermae, Dicotyledones. R. E. Owen, Government Printer: Wellington (New Zealand).

[B88] Bouček, Z. 1988. Australasian Chalcidoidea (Hymenoptera): A biosystematic revision of genera of fourteen families, with a reclassification of species. CAB International: Wallingford (UK).

[C06] Cheeseman, T. F. 1906. Manual of the New Zealand Flora. John Mackay, Government Printer: Wellington.

[DK-DW00] Downie, S. R., D. S. Katz-Downie & M. F. Watson. 2000. A phylogeny of the flowering plant family Apiaceae based on chloroplast DNA rpl16 and rpoC1 intron sequences: towards a suprageneric classification of subfamily Apioideae. American Journal of Botany 87 (2): 273–292.

[D03] Dusén, P. 1903. The vegetation of western Patagonia. In: Scott, W. B. (ed.) Reports of the Princeton University Expeditions to Patagonia, 1896–1899 vol. 8. Botany pp. 1–34. The University: Princeton (New Jersey).

Gould, K. S. 1993. Leaf heteroblasty in Pseudopanax crassifolius: functional significance of leaf morphology and anatomy. Annals of Botany 71: 61–70.

Mitchell, A. D., D. G. Frodin & M. J. Heads. 1997. Reinstatement of Raukaua, a genus of the Araliaceae centred in New Zealand. New Zealand Journal of Botany 35 (3): 309–315.

Perrie, L. R., & L. D. Shepherd. 2009. Reconstructing the species phylogeny of Pseudopanax (Araliaceae), a genus of hybridising trees. Molecular Phylogenetics and Evolution 52: 774–783.

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