Plant profiles > Dianella

Family : Xanthorrhoeaceae

Gardeners often look upon the efforts of taxonomists as a confounding inconvenience; re-naming a species here, creating another one there. However, in many instances, botanists' work in discerning the relationships between plants makes a real difference in gardens.

The recent re-classification of Dianella is an excellent case in point. From one all-encompassing entity (D. nigra), two additional species have been described - both of which (D. latissima and D. haematica) show tremendous potential as garden plants. Although these two species do not represent new discoveries in the traditional sense (they were previously considered to be part of an array of forms within the gamut of D. nigra), gardeners and landscapers were extremely unlikely to have come face-to-face with them. However, now that they have been separated out as distinct, nurseries are starting to stock material of both of them.

The tangible difference between the two new species and D. nigra (which has been retained) is the much larger size of the plants (as well as the width of the leaves in the case of D. latissima). Due to their greater stature, D. haematica and D. latissima can bring a more commanding presence to plantings. This is not to say that D. nigra is unworthy of a place in the garden. To the contrary, there are many forms of this variable species that make very good garden plants (such as the plant photographed below, growing naturally in an urban Auckland park).

The genus Dianella contains a large number of species1, and is primarily distributed around the Pacific Rim (in Australasia, southeast Asia, tropical South America, and various Pacific Islands)2. Its name is derived from Diana, the Roman goddess of hunting and the moon, and was bestowed upon it when the first specimens of the genus were grown in France3 (in the King's gardens) - where they were referred to as "dianelle des bois".

Dianella haematica
Swamp Dianella

As I wandered through Torehape Peat Dome (in the Waikato), the sight of this species growing merrily out of ditches in a recently-cleared area of peat mine offered testimony towards the potential of this taxonomic newcomer for landscape work. Within this landscape of sharp contrasts (between annihilation and regeneration), Dianella haematica is one of the first species to reclaim open ground, where its tussocks of bright green foliage stand out against the dark background of the peat.

For cultivation, D. haematica is particularly noteworthy for its impressive size (it is significantly larger than D. nigra) and its ability to thrive within wet habitats. Despite its association with damp ground (which is enshrined within its common name), it will tolerate a wide range of conditions (including average moisture levels).

D. haematica's most distinctive characteristic is the blood-red colour that is exhibited at the base of the stems - a feature that gives this plant its specific epithet. It was officially recognised as a distinct species in 2007 by Peter Heenan and Peter de Lange, two botanical scientists who have played a significant role in the taxonomy of New Zealand plants over the last two decades.

Dianella latissima

This understated, flax-like plant is one of the most exciting introductions to native horticulture of recent years. Its robust leaves, relatively large stature and graceful arching form have invited comparison with coastal flax (Phormium cookianum) - a similarity that is further reinforced by the vibrant hue of its leaves.

It has been found in a range of habitats in upper parts of the North Island, from cloud forest on the Waima Range (where the picture to the right was taken) to regenerating kauri forest and dry coastal forest (where it is often associated with kanuka, such as at Bream Head near Whangarei, where the plant in the lowermost image was growing)4.

In many places, it grows on shallow soils and disturbed ground (including rocky outcrops and slipfaces) - habitats that are analogous with the often difficult conditions presented by gardens. As testimony to this, Geoff Davidson has recounted to me how plants of this species cling to an exposed coastal bluff on Motu Kaikoura island, in the hardest conditions possible. Likewise, north-facing coastal forest and scrub at Bream Head (in which I have viewed D. latissima growing abundantly) would be prone to lengthy periods of dry conditions during the warmer months.

Within the garden, it is a valuable plant for establishing a sense of contrast (as well as order) within plantings. Although it does grow in full sun (particularly forms that have not been sourced from the benign conditions of the Waima cloud forest), plants are best provided with a modicum of shade - so that they can achieve their optimum appearance.

Unlike its relative, D. haematica (which will grow in either swampy or normal conditions), D. latissima requires a reasonably well-drained position within the garden. The specific epithet, latissima, refers to the wide leaves that help give this plant its distinguished appearance. It was described as a distinct species in 2007, by Peter Heenan and Peter de Lange, in the same paper that identified D. haematica as a new species.

 


Footnotes

  1. Outdated counts within literature of 20 years ago (or more), place the number of species at c. 25, but Peter de Lange informs me that this count is likely to increase several times over, with revision of the genus in Australia (where a potentially huge number of species occur) and the Pacific Islands.
  2. It is also native to islands of the Indian Ocean.
  3. The plants originated from Mauritius (which at that time was called Ile de France) and Réunion Island (which was then known as Ile Bourbon), and the "East Indies"; and were assigned to Dianella nemorosa, according to Lamarck's description. I do not know whether the name Dianella nemorosa still applies for that species, or whether it has become a synonym.
  4. Much of the information in this plant profile is adapted from the sole authoritative account of Dianella latissima - the paper in which Peter Heenan and Peter de Lange described it and D. haematica as new species (Heenan, P.; de Lange, P. 2007. Two new species of Dianella (Hemerocallidaceae) from New Zealand. New Zealand Journal of Botany 45 : 269 - 285).