Starfish Flower, Stapelia variegata, Apocynaceae

Stapelia variegata belongs to a select group of  plants with sapromyophilous flowers - flowers that mimic the scent (and sometimes colour and texture) of carrion, attracting fly pollinators that are deceived into laying eggs on them and accidentally pollinate the flowers as they do so. The odour of flowers with this pollination syndrome can vary - from mildly unpleasant (as in the case of S.variegata, where you need to be quite close to detect it) to truly nauseating (as in the case of Dracunculus vulgaris).

The surface of starfish flower feels like wrinkled flesh and those brown spots are rather similar to the early symptoms of putrification in a pale-fleshed corpse.The inner parts of the flower - known as the corona - are surrounded by a raised ring called the annulus and consist of five horizontal bifurcating segments and five bifurcating, upright horn-like structures, which together appear to guide wandering flies towards the functional reproductive organs, although it's not clear exactly how they do this. The male anthers on the inner corona lobes are in the form of a pollinium so are carried off in their entirety on the leg or proboscis of a visiting fly. The stigma is located within the outer corona lobes, which guide the pollinium attached to a visiting fly onto the stigma surface. You can read a plant breeder's account of Stapelia flower structure and pollination here.


Stapelia is a predominantly South Africa genus of succulent plants which used to be classified within the family Asclepiadaceae (milkweeds). This species is very easy to cultivate as long as it's planted in a well drained compost and not overwatered. This is also an easy species to raise from seed - which is worthwhile because the mottling on the flowers is quite variable - so amongst a batch of seedlings you might find something unusual and interesting.

California flannel bush, Fremontodendron californicum, Malvaceae

Until the harsh winter of 2009-10 I had a 3m. tall specimen of this lovely Californian shrub growing in my back garden, but sadly the severity of that winter killed it and I haven't yet got around to planting another. It comes from the foothills of the Sierra Nevada, thriving in nutritionally poor soil - which explains why it did do well when it was rooted close to my leylandii hedge, in a very dry spot where nothing else will grow. It's also a good wall shrub, doing well in the rubble around the foundations of a house and trained against a south-facing wall.

The flowers are interesting because, like those of hellebores, the parts that look like petals are actually the sepals - there are no true petals.

It's a very prolific producer of nectar (you can see nectar drops glistening in the image above) so bumblebees love it. 


You do need to be careful when you prune the plant though, because the densely hairy stems and leaves (which account for its name of flannel bush) can cause skin irritation. The cultivar that's most often sold in Britain is usually labelled California Glory.


The plant has traditionally been classified in the family Sterculiaceae, but modern phylogenic studies by the Angiosperm Phylogeny Group, based on DNA sequence data that gives a more accurate reflection of evolutionary relationships, place it in the mallow family - the Malvaceae. Gardeners, and sometimes even professional botanists, often deplore the way in which plant scientific names and classification change so often but they shouldn't - it reflects the fact that someone, somewhere is still taking an interest in the world's flora and that traditional taxonomic botany isn't totally moribund in universities.


Fremontodendron, also know under the synonym of Fremontia, was first discovered by General Fremont near Sacramento in 1846 and was named after him - you can read an account of the colourful life of this soldier, explorer, anti-slavery campaigner, politician and plant collector here.  

Water hyacinth, Eichhornia crassipes, Pontederiaceae

Water hyacinth Eichhornia crassipes is often rated as one of the world's top ten worst weeds, thanks to its prodigious capacity to spread over the surface of lakes and rivers. It's said that just one plant can multiply to cover an acre of lake surface in eight months, thanks to its ability to produce stolons that sprout new plants from their tips. While vegetative spread explains its local abundance, its short-lived but beautiful flowers have also played a part in its current worldwide distribution in the tropics. It comes from South America but is now a problem in Africa, India and the Far East where it has been introduced as an ornamental species that has quickly rampaged out of control. It carpets parts of Lake Victoria in Africa, impeding navigation,  and within a year of being introduced onto the Sudanese Nile in 1957 it had spread along 620 miles of river.

Water hyacinth isn't hardy in Britain, although there were a couple of reports of it surviving outside through the winter in Norfolk a few years ago. The last two severe winters would certainly have killed any plants in garden ponds, but it does make an attractive plant for a conservatory. Here it's sharing its indoor pond with another notorious aquatic weed, water lettuce Pistia stratiotes, which is equally prolific.

Water hyacinth owes its buoyancy to these inflated leaf petioles. When you cut these open ...

... you find that they are sub-divided into hundreds of small, rectangular compartments with thin walls of papery cells.

Although water hyacinth is a problematic weed there's a lot of research going in into useful applications of this plant. These include bioremediation - using its capacity to absorb and sequester toxic metals like mercury, chrome, lead, cadmium, zinc and arsenic via its fibrous root system that dangles in the water. Numerous trials have been carried out for waste water treatment. It has also been used as animal feed (from plants grown on clean water) and there's extensive research into using its rapid biomass production as a source of energy, by using the harvested plants to produce biogas or bioethanol.

Rose grape, Medinilla magnifica, Melastomataceae

Rose grape Medinilla magnifica is high on my lamentable list of 'plants that I wish I'd taken better care of'. I bought one in the spring, it flowered well through the summer, struggled through a winter in my cool  conservatory, had a final flourish of flowering in the following spring then keeled over and died. But while it lasted it lived up to its specific name and was truely magnificent. It's an excellent plant for growing in a pot on a high shelf, so that you can look up and appreciate its spectacular dangling inflorescences.

 

Medinilla magnifica is native to the island of Luzon in the Philippines, where it often grows as a large epiphytic shrub on trees. I visited Luzon a couple of times about 25 years ago, without being lucky enough to see it flowering in its native habitat - but if I could afford a fully heated conservatory with supplementary lighting in winter, it would be first on my list of plants to acquire again.

The Melastomataceae is a tropical family - you can find more on another member of the family that's much easier to cultivate as a house plant here.

Wax plant, Hoya carnosa, Asclepiadaceae

The flowers of Hoya carnosa, with their massive drops of glistening nectar, remind me of Man Ray's famous photographs of fake glass tears on a woman's face. They seem as surreal as his photographs - but are genuine enough; whenever I've grown this plant I've had to spend a lot of time cleaning off the black mould that tends to grow on leaves splashed with the sugary secretion. Apparently Victorians like to wear Hoya inflorescences in their coat buttonholes - presumably removing those sticky drops first.

Those petals are pretty extraordinary too - they look as though they're made of fake pink fur.

I've seen bees visiting H.carnosa in my conservatory but it's hard to find information on its natural pollinators in the wild. It seems likely that they are nocturnal moths because there are two published studies which show that there is a circadian rhythm of scent emission (1) and nectar secretion peaking at around midnight (2). Members of the Asclepiadaceae have an unusual pollination mechanism, where insects carry away the whole anthers, as a structure known as the pollinium, that attaches to them via an organ called a translator - similar to the pollination mechanism found in orchids. You can see sketches of Hoya pollinia here. 

Those massive nectar droplets must be the moth's reward for its exertions.

Hoya carnosa seems to have a wide distribution in South East Asia but old gardening books I've consulted indicate that it was introduced to Britain from Queensland in 1802. It's named after Thomas Hoy, who was the Duke of Northumberland's gardener at Syon House at that time. 

The plant seems to flower most prolifically if it's confined to  pots that are not too large and is kept fairly dry in winter. 

Bibliographic references: [1] Planta 174, 242-247 (1988); [2] Botanica Helvetica 116, 1-7 (2006)

Coral Drops, Bessera elegans, Asparagaceae

Garden plants drift in and out of fashion and this vibrant, late summer-flowering species seems to have been well enough known in Edwardian times to feature in popular gardening dictionaries, but in half a century of gardening I'd never encountered it - until I found its bulbs on sale in a local garden centre earlier this year. In The Illustrated Dictionary of Gardening, edited by George Nicholson who was Curator at the Royal Botanic Gardens, Kew in the latter years of the 19th. century, it's described as "an elegant little half-hardy, squill-like bulbous plant from Mexico" and Nicholson's advice for growing it holds good today, even though the 'bulbs' he mentions are actually corms. "It requires good drainage [and] .... if cultivated in pots, a plentiful supply of water from commencement of growth until ripening off", he recommended. I've grown it in pots in my conservatory, followed his century-old instructions to the letter and been rewarded this month with a display of these scarlet flowers, with their blue stamens and style. They're held aloft on 30cm.tall stems, as shown in the illustration below that must have been produced at around the time that the plant was first grown in British gardens. It deserves to be more widely grown today, even though it's not hardy - so you need to dry off and store its corms after the foliage dies down in autumn.

There seems to be some controversy about the classificaton of the plant and the Pacific Bulb Society, which has some useful information on the species, mentions that recent opinion places it in the family Themidaceae, whch I've never encountered before. Their web site illustrates a strikingly coloured purple cultivar and also mentions that Bessera may be synonymous with the very similar genus Behria: all very confusing.

[Image from Edwards's Botanical Register; Consisting of Coloured Figures of Exotic Plants Cultivated in British Gardens; with their History and Mode of Treatment. London 25: t. 34 (1839). Source: http://en.wikipedia.org/wiki/File:34_Bessera_elegans.jpg ]

Dodder, Cuscuta sp., Convolvulaceae

Mel, over at Sandy Wildlife has posted a fascinating piece about Dodder Cuscuta europaea, one of the most interesting British native flowering species, that has no root system of its own but parasitises other plants. Her post (highly recommended) is full of fascinating information about the plant and its history but I thought I would add a little about growing it. Some years ago I was given some dodder seed, which I germinated on wet paper towel (germination took about a week), then transferred the spindly seedlings to the soil surface around the base of a stinging nettle Urtica dioica plant in a flower pot. The seedlings elongate quickly and the yellow growing point rotates in a circular motion as it elongates (circumnutation) , until it touches the host plant stem. Once it makes contact there is a delay of a few days and them something remarkable happens...

........ the slender thread swells massively and then coils around the host stem. At this stage it looks more like a reptile than a plant. This transformation takes place because the dodder shoot tip has produced an invasive haustorium that has penetrated the host stem and linked up with its victim's vascular tissue, so now it can divert nutrients from its host to support the new aggressive phase of growth.

After that invasion is very rapid. The dodder branches and wherever it makes contact with the host it 'plugs-in' another haustorium - here you can see haustoria penerating the nettle stem, just a little way up from the bottom of the photo above. It often coils around itself but it seems that the haustoria can't penetrate the plant's own stems.

This is a thin transverse section, just one cell thick, cut through the point of contact between the dodder and nettle stems, seen under the microscope. The dodder stem is the darker tissue, top left, and you can see its haustorium puncturing the outer layers of nettle stem cells. If you look closely (click for a larger image) you can see the tip of the haustorium dividing into finger-like files of cells that are heading towards the host's vascular bundles (labelled V) that are conducting water, minerals and sugars within the nettle.

Once multiple haustoria have established the parasitic dodder grows very rapidly and then....

... flowers prolifically. The small white flowers are produced in clusters.  A fascinating plant - a vampire of the vegetable kingdom.