Plant profiles > Chionochloa

Family : Poaceae

The attractive flowerheads of many species of Chionochloa have increasingly summoned the attentions of gardeners over the last few years. In addition to this, they are valued for their tussock form, which in some species (such as C. flavicans) has a weeping character. The members of this genus are collectively known as 'snow tussocks'; a particularly appropriate common name, as 'Chionochloa' is derived from the Greek words for 'snow' and 'new spring growth'1.

Although some species occur naturally in areas that never receive snow, the diversity of Chionochloa species is heavily weighted in a vast range of landscapes from the South Island and montane areas of the North Island (in which snow is a regular fixture). They are essentially grasses of open habitats, such as tussock- and shrublands above the treeline, cliffs and bogs. Their range has also historically spread with the opening-up of landscapes by the activities of man2 (although more intensive farming practices are decreasing their presence in many of these modified landscapes).

The snow tussocks are very useful garden plants which, for the large part, thrive best in an open aspect with good air movement. The most commonly-used species are the weeping C. flavicans and red tussock, Chionochloa rubra. Several other species are deserving of far greater attention, including C. conspicua, C. rigida, C. flavescens, C. pallens, C. juncea and C. bromoides.

There is an interesting botanical phenomenon, called masting, which is comparatively pronounced within the New Zealand flora - most famously with rimu (whose masting is significant for kakapo reproduction), but also many other plants, including southern beech and Chionochloa. Put simply, masting is when certain plant species flower very heavily in particular years, whilst flowering lightly in the intervening periods3. There is often no set pattern to the spacing of so-called 'mast years'4 (the years in which heavy flowering occurs), giving this particular phenomenon an enigmatic character.

With regard to Chionochloa, perhaps the strongest hypothesis put forward for masting is its usefulness as a response to insect predators that eat their seeds5. By having several lean years of flowering, followed by bumper crops, the life cycles of the insects are set to the rhythms of the lean years. Although their numbers do increase during 'mast years', the plant has a better chance of having a larger quantity of seed survive the insects in these boom harvests.

A role in assisting wind pollination has also been put forward as a credible hypothesis. It may be that a range of factors are involved. Despite our frequent preference for a single, neat explanation for such things, the natural world is complex.

Chionochloa flavicans forma temata
Te Mata Peak Snow Tussock

Endemism is a word that one often reads in articles or books about plants (and nature in general). It is a very simple term, that means that a plant (or any other organism) is unique to an area. That area can be a country (many of our plants and animals are endemic to New Zealand), or it can be as small as one mountain - as in the case of the Te Mata Peak Snow Tussock.

The Te Mata form of C. flavicans is one of just two forms of this species; the other form being the commonly-planted C. flavicans forma flavicans (which grows in the east of the North Island, from Coromandel to Hawkes Bay). The major difference between the two forms is the appearance of the flowerheads; the individual florets are less densely packed on the Te Mata plant, giving them a looser, 'frothy' look. In addition, the Te Mata form often bears a glaucous (bluish) tinge to its leaves.

This is a plant of cliffs and rocky situations, which in the case of Te Mata Peak are made of limestone. Plant communities that evolve over areas of limestone are often distinctive, and frequently contain species that are unique to their locales. At Te Mata Peak, C. flavicans f. temata grows in association with two locally endemic plants, the Te Mata Pimelea (P. mimosa) and Celmisia aff. gracilenta, as well as distinctive forms of two attractive low-growing herbs6, Scandia rosifolia and Senecio banksii.

Although indicated elsewhere as being more difficult to cultivate than the more typical form of C. flavicans7, the Te Mata Peak Snow Tussock is not a tricky species to grow. When planting this species it is worth applying some knowledge of its natural growth conditions and rhythms; observations that are equally relevant to many other grass species (including C. flavicans f. flavicans).

If grasses from cliff habitats are placed within overly stable, seasonally damp conditions, they can grow too quickly, and complete their lifecycles rapidly. In the case of this species (and plants from similar habitats), it is a good idea to place rocks beneath the soil, to provide some degree of root restriction, as well as ensuring that plants receive sufficient air movement (planting specimens on a slope is of obvious value for providing this). Failure to provide some measure of environmental resistance often results in grasses, such as C. flavicans f. flavicans, being short-lived - especially in the warm, humid north.

The Te Mata Peak Snow Tussock was recognised as distinct by one of New Zealand's foremost botanists and plant collectors of the past 50 years, Tony Druce. Druce made remarkable contributions towards our knowledge of plant distribution in New Zealand, through his first-hand reports of an incredible number of sites throughout the country; as well as carrying out extremely important work on the cultivation of native plants (especially distinctive and threatened forms) at Percy Scenic Reserve.

Chionochloa rubra
Red tussock

Although a violent end may await some of the individuals in the image below, the majority seem to benefit from the army's tenure upon this land between Lakes Tekapo and Pukaki. This landscape is a fine example of just how impressive red tussock is en masse; where thousands of tussocks wave gracefully in the wind, showcasing the attractive reddish and orange tints that characterise this species.

Chionochloa rubra is a very beautiful species that can play a structural role within gardens, due to its stature (it grows to between 1m and 1.6m tall) and tough constitution. Although I associate it mostly with sites where moisture gathers (on plains, valley floors and wetland margins, as opposed to hillsides), it is very adaptable within cultivation - enduring exposed conditions and dry conditions, as well as considerably damp conditions. Having said that, it does not deal well with drought during establishment (the first year following planting).

Lawrie Metcalf, the pre-eminent expert on the cultivation of New Zealand's grasses, has made the observation that Chionochloa rubra takes on more vivid colours (in red and orange) during cold periods of the year, as well as within damp conditions.

There are three subspecies of red tussock, one of which (the northernmost subspecies, C. rubra var. rubra) is divided into two varieties. The variety that is endemic to Egmont National Park (C. rubra subsp. rubra var. inermis) is especially distinctive within the species, for the greenish colour of its leaves. The subspecies that I am most familiar with in cultivation is C. rubra ssp. cuprea, which is the variety encountered in the Mackenzie Basin, where we have planted it.

For the purposes of this plant profile, we have treated the various subspecies collectively. However, it is worth noting herein that gardeners and landscapers should look into the form that is prevalent within their own part of the country.

 


Footnotes

  1. As stated within 'Meanings and origins of botanical names of New Zealand plants (Taylor, M. 2002. Auckland Botanical Society Bulletin 26.).
  2. As outlined within 'Vegetation of New Zealand', p. 216 (Wardle, P. 2002. New Jersey, The Blackburn Press).
  3. One of the definitive explanations of masting (including hypotheses regarding its function/benefits/causes) is in a scientific paper of 1994, by a New Zealand scientist, Dave Kelly (The evolutionary ecology of mast seeding. Trends in Ecology and Evolution 9 : 465-470).
  4. In his paper, Kelly prefers not to refer to certain years as 'mast years', stating correctly that there is often a continuum of variability within the flowering of species from year to year. However, in the case of Chionochloa (and other genera), masting is so pronounced that it is beneficial to talk about 'mast years' - especially as those of us that are not scientists don't need to worry about such fine levels of accuracy (a general understanding is of more use).
    Accordingly, measuring the interval between 'mast years' can be problematic for scientists, as it requires the definition of a (possibly arbitrary) cut-off for the quantity of flowering and seeding that constitutes a 'mast year'. Once again, this should not concern most of us, as it is more important to know that masting exists, and that it has certain basic factors that define it.
  5. This hypothesis has been explored by a number of scientific papers in recent years.
  6. Technically speaking, S. rosifolia is actually a sub-shrub (and not a perennial); however, its growth form is most usefully described as being like a herb.
  7. As written within the plant profile on the NZPCN website, www.nzpcn.org.nz.