A rare groundcover on Auckland's West Coast

Over the last 18 months, we have planted a large number of this rare form of Lobelia in gardens within Auckland. It currently has informal status, and is known casually as Lobelia 'Woodhill' - the more correct botanical description is Lobelia aff. angulata (AK212143; Woodhill). Ewen Cameron discovered it at Woodhill (in dunes beneath kanuka), which is the only other population of this attractive plant - hence the tag name.

As with many groundcovers, Lobelia 'Woodhill' is a very different creature within cultivation, especially when it has access to sufficient fertility within the soil. In the wild, plants are fairly sparse. However, in gardens, it forms dense, bright green mats that are unrecognisable from the skinny runts that grow on steep ground on the Waitakere coastline.

When we first trialled Lobelia 'Woodhill' (several years ago), we planted material derived from the Woodhill population. This was a relatively weak grower, and it therefore came as a surprise when the plants from the more southerly population proved to be such a vigorous form (there are other differences between the two entities). Fertiliser is important to maintain peak condition and thick cover in the long term.

Jeff McCauley, who showed us this population and who has regularly monitored Lobelia 'Woodhill' at this site, made the point that the lack of seabirds on this coastline means that plants like L. 'Woodhill' do not get the levels of fertility that they would have received for millennia - prior to the arrival of man, and the accompanying crash in many bird populations. Therefore, plants in sites where seabirds nest are likely to exhibit the kind of vigour that it demonstrates in gardens.

This is one form of interaction between plants and animals, an important subject that Dave Kelly and other ecologists discussed at the NZPCN conference in late May. Kelly's most well-known research on plant-animal interactions concerns the fascinating relationship between birds (especially honeyeaters like tui and bellbirds) and mistletoe flowers.

Flowers and fruit are rarely seen at this population, due (as Jeff McCauley explained to us) to the depredations of rabbits, which avidly consume both. However, there were a small number of pink fruits on more inaccessible parts of the population.

The blackish stems that are apparent in the photograph below are a distinctive feature of this plant, as is the bright, light green, rounded foliage. Within gardens, L. 'Woodhill' produces flowers over a long period, from early summer to autumn.

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