Muehlenbeckia

Resistance is an attribute that this genus demonstrates admirably; whether standing up in the face of biting, salt-laden winds on our coastlines, or weaving their way through the exposed surface of braided riverbeds. Muehlenbeckia are amongst the most adaptable of New Zealand’s native plants, and as a result are a common feature of many of our landscapes.

New Zealand has five species of Muehlenbeckia, most of which exhibit a climbing or sprawling growth habit. The exception amongst these is the densely shrubby Muehlenbeckia astonii, although M. complexa can get shaped by harsh winds into forms that seem densely shrubby¹ (as shown in the picture below, on the north Taranaki coastline).

The two lower-growing species, M. axillaris and M. ephedroides, are most often seen carpeting the ground in rocky and gravelly habitats (like the mountain slope through which M. axillaris creeps, in the picture below, left). In contrast , the more vigorous species, M. australis and M. complexa can (in stable, sheltered conditions) be quite overwhelming in their growth, sometimes overrunning shrubs or small trees.

A feature shared by all of our Muehlenbeckia spp. is the appearance of beautiful small fruits following flowering. The usually translucent outer parts of these fruits are fleshy ‘tepals’ (a type of floral part, like an undifferentiated petal or sepal), which contain a hard black fruit (called an achene) at their centre. It is worth observing these fruits up close, especially on the more diminutive species – upon which the fruits are obviously, by comparison, more conspicuous.

Our species of Muehlenbeckia play an important ecological role as hosts for our native copper butterflies. These beautiful insects (of which New Zealand has several species) occupy a range of habitats, from coastal sand dunes to the mountains.

Muehlenbeckia spp. are known collectively as pohuehue. The genus derives its intriguing name from a notable physician from Alsace, H. G. Muehlenbeck, who worked on mosses and fungi².

For a shrub that is one of the most widely-planted species in New Zealand gardens and public plantings, Muehlenbeckia astonii is an elusive character within the wild. Other than at Kaitorete Spit (where the vast majority of wild plants of M. astonii endure), it is only found in small, widely scattered populations.

The first occasion that I experienced this nationally endangered species in a natural habitat was at Cape Campbell, at the southern end of Clifford Bay. In this beautifully austere landscape, shadowy mounds of M. astonii emerge from the tawny mantle of marram; accompanied by a handful of other native species that are adapted to this frequently punishing position on Marlborough’s coastline – including Olearia solandri, Ozothamnus leptophylla, Tetragonia implexicoma, Melicytus aff. crassifolius, Muehlenbeckia complexa, and Chenopodium (syn. Einadia) allanii.

As demonstrated in the image below, individual plants of shrubby tororaro assume eccentric forms in response to wind and salt – in the same way as similar species (like C. crassifolia and C. propinqua) often resemble rocks or strange beasts under equivalent conditions.

One point that is noted within the erstwhile recovery plan for M. astonii³ is relevant to the Cape Campbell population; namely, the effect of competition from other plants. Although considered a comparatively minor threat, scrambling plants like Tetragonia implexicoma (native spinach) and Muehlenbeckia complexa (pohuehue) often send a multitude of stems through the branches of M. astonii. Such associations are not purely simplistic, for competing plants also provide a measure of protection; a beneficial presence that can become smothering at a certain point. At Cape Campbell, these lianes have previously been pulled out of shrubby tororaro to safeguard against the potentially deleterious effects of competition (especially for light) – although this is not a regular activity.

M. astonii is tolerant of a wide range of conditions; from exposed positions to reasonable amounts of shade, as well as both very dry and periodically damp soils. Regarding the latter point, an interesting aspect of its ecology is that it has been recorded from ephemeral wetlands³, a surprising fact when one considers that it is normally associated with free-draining, drought-prone habitats.

At the time of our visit to Cape Campbell, two different species of copper butterfly (Lycaena salustius and L. feredayi, as far as I can tell) appeared to be sharing the habitat, as our native ‘Coppers’ often do. Large numbers of both species of these beautiful little butterflies alighted upon the stems of M. astonii. The Common Coppers (Lycaena salustius) that were present will undoubtedly gain nourishment from the large swathes of Muehlenbeckia complexa that grow at the base of the slope, whilst the presence of L. feredayi indicates that its larval foodplant, Muehlenbeckia australis (a vigorous vine of bush edges which sometimes grows in shrubby dryland communities), must be found nearby.

I was surprised to see how large the leaves were on several shrubs within this wild population, as they are normally much smaller in cultivated plants. Clumps of greyish stems/trunks emerge from the ground to support the compact, rounded shrubs. The upright, flexuous nature of these stems somewhat betrays the relationship of M. astonii to its near relatives, as the other Muehlenbeckia spp. are all climbing or scrambling plants.

My second opportunity to visit a wild population of Muehlenbeckia astonii was a much less straightforward affair than a leisurely stroll around some marram at Cape Campbell. In this case, we walked around Wellington’s infamously windy South Coast, towards Sinclair Head, on an unexpectedly calm day. A small number of M. astonii shrubs endure in an elevated, sloping basin that seems to be almost perfectly positioned to receive the full blast of southerlies coming off Cook Strait.

Working one’s way up to this precipitous position is not an exercise for the faint-hearted, and I was glad for the benign weather conditions as we wended our way through the steep bank that forms the lower part of this basin.

Although they are substantially fragmented, the asociations within which Muehlenbeckia astonii grows at this locality provide some impression of the character of an ecology in which M. astonii would have previously been more prevalent – ‘grey scrub’. On these dry, stony slopes, similarly ‘shadowy’ individuals, notably Coprosma propinqua and Coprosma crassifolia, form tight hummocks, which are adorned in parts by the intricate, deep green leaves of a distinctive, attractive form of Clematis forsteri (formerly known as C. hookeriana) that is associated with this coastline.

Of the ‘freaks and geeks’ within the New Zealand flora, this little creeper is one of the most delightfully weird on offer. It sends out a network of iridescent, spidery stems, that lend the plant an appearance of rushes flattened to the ground, or some kind of bizarre bird’s nest. Its appeal does not just lie in its curiosity value, but also in the sculptural effect created by the bright greyish-purple stems, especially when they are allowed to trail over walls or slopes.

Muehlenbeckia ephedroides is a classic example of the radical difference between how a plant looks within nature, and the form that it exhibits within cultivation. Plants viewed in the wild, such as the specimen pictured below at Rarangi Beach in Marlborough, often display the aforementioned ‘bird’s nest’ character, due to the harshness of their habitat, and the nature of the rocks through which they grow. However, plants grown within garden situations usually assume a more orderly rush-like form (either lying prone or standing semi-upright, depending on the form that is planted).

The leafless pohuehue naturally occurs in a range of sandy and gravelly habitats, such as braided riverbeds or bouldery beaches (like at Te Awanga, in Hawkes Bay, or Rarangi Beach, where M. ephedroides creates suitable conditions for the spontaneous natural gardens shown below to form). It is found in a number of scattered sites (mostly coastal) in the North Island, whereas it is far more widespread in dry eastern regions of the South Island. M. ephedroides is officially listed as ‘Declining’ in the wild, a threat ranking that reflects in part its preference for habitats that can come under pressure from human activities.

The kinds of dry, exposed ecologies to which it is adapted also host a number of other unusual, almost leafless plants, including the leafless Clematis (C. afoliata), two strange shrubby daisies (Helichrysum depressum and the lianoid H. dimorphum), and a creeping broom, Carmichaelia appressa.

As can be seen from the lowermost photo of M. ephedroides, it is not totally leafless, and can in fact bear a relatively high number of leaves – when growing in sheltered or slightly shaded conditions. The leaves, however, are the same colour as the greyish stems, and do not register as being separate (to the eye). When planted within gardens, M. ephedroides should be given a well-drained, open position. It is surprisingly amenable to cultivation as far north as Auckland, as long it is not placed in competition with other plants.

Leafless pohuehue receives its specific epithet from a perceived similarity to members of Ephedra (shrubby horsetail), a genus of rush-like plants that occurs throughout much of the Old World⁴.