New Zealand Veronica: how high do they grow?

At the moment, New Zealand’s largest flowering plant genus is Veronica (the speedwells and hebes), with 122 native and 19 introduced species (maybe 124 and 17, since we’re not sure about the biostatus of two). But pretty soon, new discoveries in Carex might knock Veronica off the top spot.

One interesting thing about native New Zealand Veronica is that—apart from the Australian V. calycina and V. plebeia that some botanists regard as natives—they’re all derived from a single ancestor that arrived here about 10 million years ago. That means their huge range of growth forms, leaf shapes, flower shapes, and capsule structures and functions have evolved here in New Zealand, likely as adaptive responses to a range of soils, climates, pollinators, and means of dispersal.

Last week, I’ve been collecting data on elevational ranges for all New Zealand species of Veronica, to add to the Flora of New Zealand text I’ve been preparing. Fortunately, the main herbaria (pressed plant collections) have digitised their Veronica labels, so I haven’t needed to look again at all the specimens (I’d already identified them).

The first thing that struck me is that only about half the specimens had a recorded elevation on the label. That’s not so surprising though; a lot of the collections are old, and it wasn’t always easy before good maps and GPS to estimate an elevation. Should I go through these and infer an elevation? I decided not to, for two reasons. First, there are already a lot of collections that do have good data, and my assumption is that those will give me a pretty accurate range for each species. Secondly, the locality data on these old specimens is often vague, and inferring their elevation might introduce errors.

Flowers of Veronica melanocaulon, from Mason River, N. Canterbury.

Indeed, I found a good example that shows the need for caution. A fairly old collection of V. melanocaulon was simply labeled “Mt Terako”. But somebody later had helpfully tried to add value by inferring an elevation for it, looking up Mt Terako on the map to give a databased figure of 1740m. When I compiled the data to get overall ranges, this was the highest elevation for V. melanocaulon by about 800 hundred metres. V. melanocaulon plants are found along river and stream banks, not on mountain tops, and while I have no doubt it was collected in the general area of Mt Terako, I’m also sure it wasn’t at 1740m.

Veronica elliptica, at Milford Sound.

About 30 species can be found at or near sea level, but only a few—like V. elliptica at 0–45 m—are strictly coastal. Many, like V. odora, have larger elevation and habitat ranges that only sometimes come as low as sea level. V. lilliputiana plants grow on silty or muddy shores of lakes and ponds and only sometimes find suitable sites near the sea, for example in lagoons at Lake Forsyth and Otago Peninsula.

Veronica lilliputiana (scale = 1 mm).

At the other end of the spread, Veronica achieves some of the highest elevations for flowering plants in New Zealand. At the very top is V. birleyi. Its lowest record is 1830 m, and it has been collected as high up as 2835 m. I’ve only seen it once, at Copland Pass near Mt Cook, and then only because a couple of climber friends took me there safely. I once thought I’d found V. birleyi at 1470 m on the Takitimu Range in Southland, but closer examination showed those plants were a new species, V. spectabilis, that’s most likely its nearest relative.

Veronica birleyi (left) has smaller flowers (not shown) than the similar V. spectabilis.

Veronica epacridea is a close second, reaching an elevation of 2745 m, but it has a larger range, down to 638 m. The high altitude veronicas are mostly members of the snow hebe and connatae informal groups. Nine species or subspecies are not known at or below 1200 m, roughly the old 4000 foot mark, and eight (not always the same ones) reach maximum elevations of 2000 m or more.

Veronica epacridea on the Torlesse Range, Canterbury.

What’s in between? The bulk of the genus is neither coastal, nor high alpine. How many are subalpine to alpine versus lowland to montane? We could use the natural tree-line as a convenient dividing point, except that it varies, from 1500 m in central North Island, to 900 m in Southland (Alan Mark’s “Above the treeline” has a good introduction to the alpine zone and its environments). I can’t be bothered going through my list one by one to assign them carefully to “above” or “below” tree-line groups, otherwise I’d probably be writing this as a scientific paper, not a blog post.

About 65 species and subspecies have a minimum elevation above 600 m and a maximum over 1500 m, so they’re mostly found in the zones above tree-line. And about thirty native species and subspecies have maxima that are below 900 m, so they’re lowland to montane. Another thirty or so have maxima clearly above, and minima clearly below tree-line; they seem to be plants of the montane to subalpine zones.

Veronica epacridea has the biggest overall range, at 2107 m. That’s because, although it’s mostly an alpine to high-alpine plant, it can be found occasionally on screes and cliffs at much lower levels, perhaps establishing sporadically from seeds or even bits of plant that have blown down from above. V. lanceolata also has a wide range (1708 m). It has narrow-leaved forms found at low altitudes in coastal Taranaki and Coromandel and forms with broad fleshy leaves in the North Island mountains. Its local populations are maybe adapting to different conditions and could be in the process of diverging into separate species.