Wednesday, 31 July 2013

Wednesday wildflower: old man's beard.

“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).

Old man's beard still must go, but let's hope no native Clematis get pulled out instead by well-meaning weed-busters.  The Flora treatment for their identification is on line at Landcare Research's website and you can find pictures identified by botanists at the Naturewatch site..

Monday, 15 July 2013

Wednesday wildflower: winter heliotrope

Winter heliotrope isn't a true heliotrope, but a daisy, related to the senecios I've featured in a few other entries in this series (here and here).  But it is both a wildflower and a weed, a garden plant that has escaped.
Winter heliotrope, Petasites fragrans.

This patch was in Aro Valley, an old-established part of Wellington, originally working class but now a mix of gentrified old cottages and student flats, arty cafes and boutiques.  The plants were in a garden that had a rather wild appearance; I'm sure its owner was deliberately aiming for a wilderness look.
Winter heliotrope flower heads.

The flowers are pink, instead of the usual yellow for this tribe of daisies (Tribe Senecioneae, characterised by the involucral bracts being in a single row, not in overlapping rows like roof shingles).  Winter heliotrope is dioecious (has separate male and female plants), but all the plants in New Zealand are males.  Their outer ray florets are all sterile (they make neither pollen nor seeds); ray florets are female in most daisies (the general structure of daisy flower heads is explained here).  The inner disk florets are male (often hermaphrodite in other daisies).  Not being able to have sex doesn't deter this plant a bit, because it is able to spread vegetatively, and of course people deliberately and inadvertently help that process.

You might note the stigmas in these florets, the large white somewhat feathery things poking through the tube of purple anthers in the centre of these florets.  How come male florets have such a large stigma?  In this and several other families, the pollen is presented on the stigma, so even though the florets are male, they still need well-developed female parts for pollen dissemination.  In a hermaphrodite daisy floret, the stigma opens after the pollen has gone to expose the two receptive surfaces.  I didn't examine these closely at the time, but in the photo I can't see any that have opened.

Wednesday, 3 July 2013

Wednesday wildflower: German ivy, Delairea odorata

It's Thursday evening in New Zealand, but it's still Wednesday on the west coast of North America and the eastern Pacific, so if I'm quick I can post a Wednesday Wildflower on time.  I haven't posted here much lately, but I'm working enthusiastically on a new project that I'll write about soon.
German ivy on a bank in Karori, Wellington, with broom, Cytisus scoparius.
Delairea odorata is a climbing senecioid weed that's native to southern Africa and common around Wellington and tends to flower in the winter.  It sprawls over banks and other plants.
Some of the flower heads of a panicle of German ivy (iPhone with Ōlloclip macro)
The flowers are in small heads and there are no ray florets, only disc florets (compare with my post on the distantly related Roldana).  The small heads are arranged into larger panicles that are quite showy and rather unpleasantly scented (in my opinion; it's very subjective).
A single capitulum (head) of German ivy.  Note the absence of petal-like ray florets and the evident filaments at lower right.
Under the microscope, you can see how the anthers are joined together in a tube that surrounds the style, but the filaments (anther stalks) are separate.  That's a characteristic of the whole family.  The senecioids (Tribe Senecioneae) are characterised by having their involucral bracts (the sepal-like leaves that surround the base of the head) all in a single row.