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Friday, December 24, 2010

Hydrangea spp., Hydrangeaceae

Season's Greetings and Best Wishes for 2011 to all readers of this blog.

I know some people who think that Hydrangea flowers are more attractive when dead that alive. It's a sentiment that I have some sympathy with...

... because I don't find the heavy, long-lasting infloresences of mop-headed Hydrangea macrophylla cultivars particularly attractive, but when winter has done its work on the dead flower heads the skeletonised florets, like those in the first photograph, are transformed into something rather delicate and beautiful.

Hydrangea infloresences are an interesting example of division of labour, where the central mass of short-lived fertile flowers, bearing stamens, stigmas and ovaries, have no particular visual advertising to attract insects but devolve that job to the large sterile florets, that surround the edge of the inflorescence like orbitting satellites. Petals wilt as soon as a flower is fertilised but since that outer ring of sterile advertising florets can never be fertilised they last indefinitely, throughout the whole flowering period and often right through the winter as skeletonised petals.

The arrangement is delightful in some of the larger species like H. aspera (also known as H. villosa) when it's grown in an open, woodland garden.

Advertising all those fertile florets with just a handful of sterile florets is a very efficient way for the plant to attract its pollinators, but it's hardly surprising that plant breeders have hybridised and selected species for large numbers of sterile, long-lasting florets for maximum impact in a shrub border, reversing nature's economical use of advertising in the quest for maximum visual impact.

Monday, December 20, 2010

Tephrocactus articulatus var. papyracanthus, Paper-spined Cholla

This must surely be one of the most intimidating of all plants - the Paper-spined Cholla Tephrocactus articulatus var. papyracanthus. It comes from Argentina and those sabre-shaped spines that look so lethal are about eight centimetres long, but they're not as dangerous as they look. They really are like paper and simply bend under the slightest pressure; you'd be hard-put to draw blood with them. The tufts of tiny bristle-like hairs called glochids that you can see at their base are far more of a problem. They have barbed tips and are intensely irritating when they embed themselves in your fingers.The easiest way to remove them from flesh is to use a piece of adhesvive tape to pull them out.

Paper-spine cholla ( or the 'Edward Scissorhands' cactus, as my kids used to call it) is a slow-growing relative of the prickly pear cactus and is easily propagated by breaking off one of the jointed stem segments and rooting it in well-drained, gritty compost - but be sure to watch out for those nasty little glochids.

Thursday, December 16, 2010

Clematis cirrhosa

My Clematis cirrhosa, whose straggly stems climb through a crab apple tree in my garden, managed to produce just this single flower before the first spell of freezing weather arrived. There are more well developed flower buds on it but the icy weather has returned and it's doubtful if they'll open now. Bearing in mind that this species hails from the Balearic Islands it's a small miracle that it survives here at all. It came through last winter safely so I'm optimistic that it'll do so again.

In milder parts of southern England there have been several reports of bumblebees that emerge on mild days in mid-winter visiting these flowers, along with Mahonia blossoms, but that's unlikely during this winter's icy blast.

Monday, December 6, 2010

Chinese lanterns,Physalis alkekengi var.franchettii

My grandmother in Sussex used to grow Chinese lanterns Physalis alkekengi var. franchettii to perfection, but I've always struggled to grow them up here in North-East England, not least because the slugs and snails zero in on them almost as soon as new shoots appear in spring. Looking at the natural distribution of the plant - southern Europe and eastwards across drier parts of Asia, it's not surprising that I haven't been able to grow these well. Gran's garden was mostly flint and chalk and she grew them in a sun-drenched spot in gravel at the base of a south-facing bay window, which provided a fair approximation of the Mediterranean climate and soils that this plant enjoys.

The orange papery 'lantern' is formed from the sepals (collectively the calyx) of the flower that inflates once it has been pollinated, enclosing the....

......shiny red berry within. The dried plant makes a colourful winter decoration but if you leave some outdoors the softer parts of that inflated calyx rot away surprisingly quickly, so that by Christmas you have ....
... only the skeleton of veins left which - with a light spray of gold laquer - makes a delightfully intricate Christmas tree decoration.

There seems to be some taxonomic uncertainty surrounding this plant, which is sometimes known simply as P. franchettii. According to the late Graham Stuart Thomas - a gardener who really knew his perennials - P. franchettii has more pointed lanterns - like those in the first photo above - compared with the rounder P.alkekengi, in the skeletonised example above but, since he also mentions that they hybridise, it's reasonable to conclude that they are merely varieties of the same species.

Wednesday, December 1, 2010

Madagascan Lace Plant, Aponogeton madagascariensis

I've never seen a living specimen of Madagascan lace plant Aponogeton madagascariensis but I found this pressed specimen in the herbarium of Durham University's School of Biological and Biomedical Sciences. I suspect it's a very old specimen as it still bears an old Latin name for the genus, Ouveranda. These look like skeleton leaves but in fact they are intact - during the final stages of development of the expanding leaves of this aquatic plant the cells between the veins die, during the process of programmed cell death (apoptosis) leaving a network of veins surrounded by living photosynthetic cells. The development of the leaf has recently been studied in great detail and you can read the scientific paper from the American Journal of Botany that describes the process (which also includes photos of the whole, living plant) by clicking here.

In this close-up of a portion of the pressed leaf you can see the ladder-like arrangement of leaf veins that are surrounded by photosynthetic tissue. Apparently this plant is a popular but challenging species to grow for tropical aquarium enthusiasts and you can read an account of its cultivation here.