“Old man’s beard must go,” said the not-so-young bearded botanist David Bellamy some years ago on TV, and we all knew this was a serious weed that threatened to smother our native forests. Since then, it’s not as common as it used to be. The efforts of the Department of Conservation, local and regional councils, community groups, and individual landowners have largely seen off the worst infestations in many places. But around Wellington city, and probably many other places, there are little pockets of old man’s beard everywhere. My guess is it’s waiting for our vigilance to let up and it’ll be back with a vengeance.
|Old man's beard fruits, Northland, Wellington.|
Old man’s beard is called traveller’s joy in England, which goes to show that one country’s wildflower is often another’s weed. The local name refers to the fluffy white plumes on the seeds. More accurately (with my pedantic botanist’s hat on) these aren’t seeds but fruits, each bearing a single seed inside a loose-fitting fruit wall. The flower, like many in the buttercup family, has multiple separate pistils, each with its own ovary, style and stigma. After pollination, the pistils from a flower mature into a cluster of separate 1-seeded fruits, each with the fluffy remains of the style to form a plume that assists in wind dispersal.
One of the practical problems with a public eradication campaign is that people need to be able to recognise the target weed, and not try to eradicate look-alikes. Many people worry that they might be pulling up one of the native Clematis instead, so I thought this week a few notes about these plants might be useful.
First, old man’s beard (Clematis vitalba) is one of just two species in New Zealand with once-pinnate leaves; they have a central axis with a terminal leaflet and two pairs of lateral leaflets. The other species that’s characterised by once-pinnate leaves is C. maximowiciana, but its leaves are more leathery than the leaves of old man’s beard; also it has larger flowers, 30–50 mm diameter. Most of the other species have three leaflets although these can be quite finely divided. Two species, C. tangutica (yellow flowers) and C. flammula (white flowers), have twice-pinnate leaves (the pinnae [leaflets] are themselves pinnately divided). The native C. afoliata has no leaves at all, just the leaf stalks that twine around supporting shrubs’ stems.
|Old man's beard flowers, Kakariki, Manawatu. They are mostly 12–25 mm diameter|
Secondly, the introduced species mostly have 4 sepals in each flower, but many (not all) of the native ones have six. All the introduced Clematis have hermaphrodite flowers (with functional stamens and pistils) whereas the natives all have unisexual flowers on separate plants (flowers have either stamens or pistils, but never both).
|Clematis forsteri, a native species. Pale yellow male flowers with 6 sepals. If you see these, don't just look, sniff too: many are sweetly scented.|
Most of the native Clematis flower in the springtime or even late winter (some plants of C. forsteri are in flower now in late July). Old man’s beard is a summer-flowering plant, mostly from December to May.
|Clematis paniculata, another native species, male flowers.|
Old man's beard flowers are greenish white. Most natives have pale or greenish yellow flowers, although the large (and unisexual) flowers of C. paniculata are pure white, C. marata and C. marmoraria are white or greenish, and C.
marata quadribracteolata (corrected 4 September 2013) brown or purplish brown. Finally, the introduced Clematis are all deciduous whereas the natives are all evergreen (except poor C. afoliata, which hasn’t got leaves to lose).