Senecio

One of the pleasures of spending a lot of time around native plants is that, over time, you notice more and more layers in ecosystems. For many of us, one of the last layers to unfold is the ephemeral presence of herbs, like our many native species of Senecio.

This interesting genus is one example of the many frontiers that Oratia Native Plant Nursery pushed over several decades, with regard to introducing New Zealanders to their natural heritage. Plants like our Senecio spp. do not fit readily with the kinds of static designs that are favoured by many landscape designers; and it is against this kind of template that the garden merits of plants are often weighed.

However, Oratia Native Plant Nursery’s approach, rather than reducing the gardenworthiness of plants down to a limited range of criteria, is to celebrate the qualities that our many and varied native species possess. This manner of looking at plants requires an innovative attitude to how one uses plants, and (very importantly) provides the basis for work in which a great number of our rare and threatened species can be appreciated within gardens.

Other than Oratia Native Plant Nursery, the only other grower to have made serious attempts to bring one of our Senecio spp. into cultivation (in any numbers) is ‘Plant Hawke’s Bay’ – a nursery run by Marie Taylor, in Napier (with the aim of providing Hawke’s Bay locals with a stimulating range of plants sourced from their region). Marie grows the highly attractive Senecio banksii (pictured above), a plant that is not dissimilar in its overall form to the commonly-used exotic, Lamb’s Ears (Stachys lanata). More information is provided on S. banksii further down in this profile.

New Zealand has around 20 native species¹, of which 13 are found nowhere else in the world. For the purposes of cultivation, the species that have the most potential are Senecio banksii (especially the form that has historically been differentiated as S. colensoi), S. rufiglandulosus, S. radiolatus, S. sterquilinus, S. glaucophyllus ssp. basinudus, S. dunedinensis and S. quadridentatus. With the exception of the last two species, all of these bear bright yellow flowerheads, at various times of year. As a general rule, they should either be trimmed back hard after flowering (and seed-set, if that is required), or removed, where they are to be used as annuals (ready for the emergence of the next generation).

I would also add the critically-endangered S. scaberulus to this list, with the proviso that its greyish-green foliage should be cut back hard once it has achieved its full height (as it will become scruffy thereafter). This listing of suitable species does not mean to imply that other Senecio spp. are unsuited to garden use; it is just a selection of the species with most potential. For example, a plant like S. marotiri could act as a small, ephemeral detail within the gardens of native plant enthusiasts.

The name of the genus, Senecio, is derived from the Latin term for ‘old man’ (senex). This probably refers to the whitish, hairy seedheads that members of the genus bear, which are somewhat similar in character to an old man’s beard.

This attractive, ground-hugging plant is one of the most unexpected surprises that I have ever come across in our natural environments. I have only encountered it at Te Mata Peak (although it occurs at other places on the North Island’s eastern coastline); and upon viewing it there, I was immediately impressed by its substantial, greyish green, woolly foliage.

S. banksii is essentially a plant of cliffs, and should be afforded a similar position within gardens (i.e., one with sharp drainage, and ideally some air movement). It is quite adaptable to a range of aspects. I have noted it growing in full sun within cracks on boulders or outcrops (almost as tough a situation as one can imagine), and tumbling in fairly deep shade at the base of south-facing cliffs (where the clumps of foliage were much fuller and greener).

Plants produce vibrant yellow flowerheads throughout summer, which have a typical daisy appearance to them. It is a variable species, that was previously classified as belonging to two separate entities. The woollier forms (such as that present at Te Mata Peak, pictured above, left) were designated as S. colensoi, whilst other smooth-leaved forms have always been named S. banksii.

Senecio banksii occurs naturally from the Bay of Plenty down to the Wairarapa, and is mostly found near the coast. It is particularly associated with limestone, the substrate on which it thrives at Te Mata Peak.

The name ‘cotton fireweed’ may not inspire a great desire to plant this species in gardens. However, its silver foliage makes it a very attractive plant that may be employed as a gap filler within native gardens.

It has been used to very good effect at the Arataki Visitors’ Centre (in the Waitakeres), in a thick grouping of plants that showed off the silver foliage beautifully. In this case, it was reminiscent of silvery clumps of Celmisia leaves.

This little herb reaches up to 1m tall when in flower, but the foliage is generally only 10cm to 30cm tall for most of its lifecycle. The flowers are quite inconspicuous, and can (in my opinion) detract from the appearance of plants. For this reason, it can be beneficial to trim flower heads right back to the base, once they have reached maturity (unless fresh seed is required). It should be noted here that S. quadridentatus self-seeds freely; popping up in disturbed ground as it does in nature.

Cotton fireweed occurs naturally throughout much of the country. I particularly associate it with steep earth banks and rocky places, where it readily finds the open ground that it requires.

For floral impact, this vibrant character is the pick of the genus within New Zealand; and furthermore, I would rank it as one of the most spectacular of our flowering plants. Not only are the flowerheads substantial (in the region of 20cm in diameter); they are also presented well clear of the basal rosette of foliage. The spear-shaped, soft green leaves of this herb also add to its appeal, yet curiously it has never found its way into our gardens.

Senecio rufiglandulosus grows mostly in damp, relatively open habitats from Auckland’s Waitakere Ranges (where it is known from a very small number of plants) to north Westland. It is found at a range of altitudes, from lowland sites (including coastal habitats) up to subalpine areas.

One observation that a colleague of mine has made about this species is that it may thrive best when supplied with a high level of fertility, as it would have historically received in many of its sites from the rear end of seabirds. This is a reasonable assumption for many herbs that grow in coastal plant communities (as S. rufiglandulosus does within the Auckland region, and in other parts of the country).

In my experience of growing this plant, Senecio rufiglandulosus prefers a moist position in partial shade. If the ground dries out too much in mid-summer (when it is in flower), stressed plants can suffer from rust – a fungus that can weaken plants. This is also exacerbated by high humidity levels, which is obviously of greater relevance in northern areas of New Zealand.

Where humidity is a factor, it is a good idea to plant this species in a position where it receives a good amount of air movement. This is less of a consideration the further south one moves through the country, as exhibited by the ease with which we have cultivated S. rufiglandulosus at Waikereru Ecosanctuary near Gisborne.

It is perhaps a reflection upon its beauty (as well as the timing of its flowering, admittedly) that S. rufiglandulosus  was collected (and even illustrated by Joseph Banks and Daniel Solander’s artists) on Cook’s first voyage to New Zealand, in 1769.