Plant profiles > Libertia

Family : Iridaceae

Irises hold a special place in the affections of gardeners. Their flowers are simultaneously simple (in form) yet complex (in the patterns that they bear), and mesmerise us in the same way they attract the pollinators for whom their show is intended.

This well-known family extends to New Zealand through the presence of Libertia, a genus that has taken on considerable horticultural significance in recent years. In contrast with what one might expect (considering the family to which it belongs), Libertia's newfound popularity is not primarily based on the abundance of simple white flowers that our native irises produce. Instead, it is the sword-like, evergreen foliage that has endeared it to gardeners and landscapers, as it can provide order to lower tiers of planting compositions.

The first member of the genus to receive widespread attention was Libertia peregrinans, for rather obvious reasons - its burnt orange foliage colour is an unusual and striking asset. Although common in cultivation, this predominantly coastal species (which is pictured below, growing on a Southland sand dune) is now threatened in the wild. As with other threatened species, gardeners and landscapers should be encouraged to plant seed-grown material of L. peregrinans, to help in maintaining diversity in the species (especially from locally-sourced stock).

Another threatened species, the critically endangered L. cranwelliae, is becoming increasingly popular due to the appeal of its upright, often yellowish leaves and creeping habit. This elusive character was presumed extinct for decades until an East Coast DoC ranger, Graeme Atkins, rediscovered it in the wild (in 2006).

In relatively recent years, botanical research has doubled the number of Libertia species within New Zealand to eight. Most are well adapted to cultivation, within a variety of situations. A general rule for our Libertia spp. (with the exception of Libertia peregrinans) is that they usually perform best when afforded a small amount of shade. Too much exposure to sun and wind can result in plants that have brown leaf tips, an effect that rapidly lends plants a scruffy appearance.

Aside from the two mentioned above, the most popular species for garden use are L. ixioides and L. grandiflora (whose flower is pictured above). L. ixioides has become especially widely used over the last few years, due to the introduction of a number of coloured cultivars/selections, and may well be the top selling 'species'1 in the country now.

The genus receives its charming name from a nineteenth century Belgian woman, Marie-Anne Libert, who studied mosses, lichens and their unassuming relatives2. Its distribution alludes to an origin within the ancient supercontinent, Gondwanaland, as it occurs only in the Southern Hemisphere - in New Zealand, Australia, New Guinea, Chile. New Zealand hosts the greatest diversity of species, with 8 of the c. 13 species restricted to our shores3.

Libertia grandiflora
Mikoikoi; New Zealand Iris

Plant species are often distinguished by minor differences. Nonetheless, these differences are usually somewhat simple to discern, with a little specialist knowledge. And then there are cases like L. grandiflora. I like to think that my botanical knowledge is fairly good, but this species is so similar to L. ixioides (especially under slightly shaded conditions) that it left me befuddled as to its precise identity (despite being in flower).

I suspected that it was L. grandiflora, from the overall cut of its jib, but it was not until I enquired with New Zealand's leading authority on the genus that I could unequivocally describe it as such. So why is all this botanical hairsplitting important ? Because the cultivation requirements of L. ixioides and L. grandiflora differ (especially with regard to the forms selected for gardens), and because the floral display is often markedly different on these species.

Generally speaking, Libertia grandiflora's flowers are more conspicuous, as they are usually held above the foliage. In contrast, L. ixioides normally bears its flowers well within the leaf fans. Another key difference is that the 'petals'4 on L. grandiflora are generally more rounded, whilst the seedheads also help to separate these species.

Although it has, within horticultural literature, been described as suited to a position in full sun, that has not been my experience (nor that of colleagues of mine). Plants growing in a completely open aspect tend to look scruffy; and it is therefore better placed in a situation where it will, at the least, receive dappled shade for part of the day. Libertia grandiflora is quite capable of withstanding dry soil conditions, as evidenced by the plants photographed above, that were growing on a roadside bank at the north end of the Waitakeres.

 


Footnotes

  1. 'Species' is written within inverted commas here because I cannot say whether various cultivars that are ascribed to (or derived from) L. ixioides have been hybridised with other species (or arisen from natural hybrids) during their development.
  2. As stated within 'Meanings and origins of botanical names of New Zealand plants' (Taylor, M. 2002. Auckland Botanical Society Bulletin 26.).
  3. The worldwide number of species is difficult to ascertain accurately. Blanchon et al. (2002) give the total number of species as c. 12, but this was before the description of L. flaccidifolia ('A taxonomic revision of Libertia (Iridaceae) in New Zealand'. New Zealand Journal of Botany 40 : 437-456.).
  4. These are actually tepals; but due to the difference between the inner tepals and outer tepals in Libertia, the terms 'petal' and 'sepal' are sometimes applied for describing them.