Splitting hairs and pulling teeth

October 2, 2017

Although botanical accuracy is important to us, we don’t tend to pursue the same level of detail as professional (or even many amateur) botanists for picking the fine differences between plants. In the case of most plants that we specify in our designs, they are relatively easy to discern on sight; especially once you ‘have your eye in’ for recognising them.

However, in the case of 2 nationally threatened species that I viewed in the wild over the weekend with friends, it was necessary to look into minute details (whether hairs on the petioles or teeth on the leaf margins) for having confidence that we had found the plant in which we were interested.

The first of these is a rare geranium, called Geranium retrorsum (shown above, left), which endures in an intriguing remnant of lavafield in the midst of one of Auckland’s most intensely populated industrial areas (where Coprosma crassifolia also still grows in the place where it was first collected by William Colenso in 1842).

We have a considerable interest in this subtle species of dry habitats (pictured above, in flower) due to our work on the 1769 Garden at Longbush Ecosanctuary, where we have planted it in stone mounds (along with other species that Banks and Solander collected on their first days ashore in Aotearoa in 1769).

Both Geranium retrorsum and another rare native geranium (Geranium solanderi, pictured below) grow in crevices within the beautiful lava blocks at this Auckland remnant, where their thick central roots (which are shaped like turnips or carrots, depending on the species) provide them with the ability to withstand the drought conditions that are obviously present in summer.

Due to the presence of both of these similar species, we needed to look into the hairs on their petioles (which, in G. retrorsum, are self-evidently retrorse, meaning that they are folded back over) in order to say which species is which. Having spent some time looking at both geraniums, it became clear that they are (at least in this location) quite easy to tell apart in terms of their overall appearance, with G. solanderi having a larger leaf and more robust character.

Similar attention to detail was necessary for a walk up Mt Tamahunga (near Matakana and Leigh) to see a critically endangered ‘native iris’ called Libertia flaccidifolia (pictured below, growing on a rock). Although there is a clue in its name (‘flaccidifolia‘ refers to the weeping foliage), one other way of distinguishing this relatively recently described species from Libertia ixioides is the scabrid (meaning rough) leaf margin.

By running one’s hand along the leaf margin, one can discern L. flaccidifolia‘s rough leaf margin, which is the result of fine tooth-like projections. In the case of this species, that distinction really was very minor, to the extent that I came away feeling that a better way of recognising this species (when not in seed) is on the basis of its broad, floppy foliage (the colour of which also seemed to be paler than the L. ixioides down the hill).

On the way to the summit, we also had the pleasure of seeing some very mature plants of Melicope simplex that had assumed a gnarled, tree-like structure (as shown below), in contrast to the shrubby habit that we are more accustomed to seeing from M. simplex. As is often the case with Melicope simplex, the group of plants that we saw were growing in a confined area, where skeletal soils seemed to contribute to a comparatively open habitat amidst the surrounding forest.