Winter fragrance

In these cold, grey days after Christmas, in the depths of winter, any flower is welcome, although I do have some reservations about this one - winter heliotrope Petasites fragrans

 I planted a small cutting  in our front garden many years ago for nostalgic reasons, because it grew on a roadside near my home in Sussex when I was a child. Its creeping underground rhizomes have spread relentlessly outwards, defying attempts to dig it out because it regenerates rapidly from small rhizome fragments left behind. Fortunately, it's confined by two walls and a concrete path, which limits its opportunities from further escape, but I can see why people warn against introducing it into cultivated soil. 

It has become naturalised in many places throughout Britain, moved around in dumped garden soil, around waste tips or where it as been fly-tipped on roadsides.

On the plus side, winter heliotrope has a delightful fragrance, variously described as resembling vanilla, almonds or marzipan, so when it flowers in January I always keep a few inflorescences on the window ledge in a vase. 

It originates from the central Mediterranean region and North Africa and was  introduced into gardens here in 1806, then first recorded in the wild in Middlesex in 1835. My favourite naturalised population is on the edge of the sea cliffs near Noses Point at Seaham on the Durham coast where, on a bright winter's day, it looks wonderful with the North Sea as a backdrop.

Himalayan balsam nectar

 Himalayan balsam is notoriously invasive and the chances of ever eliminating it on a large scale seem negligible. Even when plants are pulled up there is always a large seed bank in the soil, and flooding carries the seeds far and wide along river valleys. But it does have at least one virtue: it's a very rich source of nectar late in the year, when few native nectar-rich plants are available. Bees and wasps find it irresistible.  

The flowers have a distinctive pollination mechanism, with anthers positioned in the roof of the flower, so they deposit pollen very efficiently on the upper thorax of visiting insects, like the honeybee above and the wasp below.

Persistent insect visitors are immediately identifiable by the dense coating of pollen that they carry from flower to flower - a very efficient pollination mechanism which goes a long way towards explaining the high levels of seed production.

Some balsam nectar-addicted visitors, like the wasp above, become so heavily coated in pollen that they develop a ghost-like appearance. 

 These old Cotoneaster bushes are rooted in fissures in the limestone cliff behind Ashes quarry are Stanhope, in Weardale. Cotoneaster is a genus with many species, mostly from Eastern Asia, that has long been cultivated in Britain for its attractive berries in autumn; these plants would undoubtedly been of garden origin, originally arriving in the quarry in bird droppings. Although almost all berries in the dale have now been eaten by birds, this heavy crop remains almost untouched. This happens every year, and there is no obvious reason why birds should not have taken them. Maybe a flock of redwings or fieldfares will find them soon.

 

A Rapidly Evolving Botanical Hooligan......

Invasive species often hit the headlines here in Britain but we have exported a few of our own too, that have created ecological chaos in other countries. One of the most notorious is purple losestrife Lythrum salicaria. Here in the UK it's a well-behaved wetland species and the Wildlife Trusts' web site describes its 'impressive spikes of magenta flowers' as a 'valuable source for long-tongued insects like bees, moths and butterflies, including brimstones, Red-Tailed bumblebees and Elephant hawk-moths' 

In our garden it's a star performer in a small, boggy area where it's particularly popular with hoverflies ...

.... that feed on its readily accessible pollen. It does have a very high potential seed output, so most gardening experts advise removing the dead flower heads before they can set seed but in the wider countryside it's a well behaved component of our native wetland flora and is sometimes deliberately introduced to increase botanical biodiversity, as it has been .....

...... here along the Ouseburn in Newcastle, bringing a splash of colour to what was once a heavily industrialised and polluted environment.

However, when it travels abroad it develops hooligan tendencies, spreading rapidly and outcompeting native vegetation. Since it was first introduced into the New World in the New England area, probably sometime around 1800 in ships' ballast (and also deliberately because of its uses in herbal medicine) it has run riot, with a very rapid period of range expansion in the 20th. century. It's now the worst invasive plant species in wetland ecosystems throughout the eastern seaboard of the US and in Canada. You can read a detailed account of the history of purple loosestrife in North America and Canada by clicking here

Several theories have been advanced to account for its invasive behaviour, one of the most important being that when it travelled across the Atlantic it left its natural pests and diseases behind, so that it could reach its full reproductive potential. A single vigorous plant can produce fifty flowering stems that dominate surrounding vegetation and produce around two million seeds - which are carried far and wide by wind and water - annually. Once established in its new environment, and free of pests and pathogens, purple loosestrife no longer needed to devote energy to defending itself and could commit all its resources to reproduction.

Recently a research paper in the journal Science has provided another insight into the invasive tendencies of this New World immigrant. Multiple introductions of purple loosestrife produced a genetically variable population that has rapidly evolved ecologically adapted populations across a very wide geographical distribution. Plants that have colonise Canada, where the growing season is short, have evolved to flower early to maximise their seed output. Those that have migrated into the warmer southern United States have evolved to flower later and devote more of their resources to tall, vegetative growth before they switch into flowering mode. The authors of the research reciprocally transplanted sample plants from the extremes of their range to confirm the evolution of this rapid local adaptation; predictably, early bloomers from the north were less competitive in southern locations, and vice-versa.

One of the most interesting wider implications of this research is that it highlights the ability of plant species like purple loosestrife, that are genetically variable, that have a vast seed output and that reproduce rapidly once established, to evolve adaptations to new environments very quickly. Now that we are in a period of rapid climate change, it does give an indication of the ability of some plants to use their pool of genetic variation to exploit changing environments by evolving new adaptations, and it underlines the importance of maintaining genetic variability in plant species that might be vulnerable to climate change.


Source: Robert I. Colautti and Spencer C. H. Barrett (2013). Rapid Adaptation to Climate Facilitates Range Expansion of an Invasive Plant. Science 342, 364

A Beautiful Menace

This colourful display of Rhododendrom ponticum fills a little valley between the high pastures and the moorland to the south of Wolsingham in Weardale. The plants almost certainly originated in the grounds of the nearby St. John's hall, once the home of the Backhouse family who were bankers, tree planters and horticulturists who became famous as producers of new daffodil cultivars. The progeny of their old daffodil varieties fill the grounds around the hall in spring and at this time of year Rhododendron blooms that were once merely decorations beside the long drive leading up to the house fill the woodlands and these little moorland edge valleys. There would probably be more of them, but for the incredibly high rabbit population hereabouts that must limit the establishment of seedlings.

R. ponticum was introduced into Britain from Spain in 1763 and soon became popular with owners of large houses with extensive grounds. Cragside, home of Lord Armstrong in Northumberland, is still famous for its Rhododendron display. 


Unfortunately the plant is very invasive and has been colonising woodlands and sheltered valleys on acid soils ever since it first escaped into the wild in 1894, smothering all natural vegetation of lesser stature in its dense , evergreen shade. The genus is noted for its interspecific hybrids, many of great garden merit, and in some parts of Britain R.ponticum seems to have hybridised with the North American species R.catawbiense, producing offspring with even greater environmental tolerance.

Rhododendron ponticum floral displays are at their best at this time of year and their abundant nectar usually attracts large numbers of bumblebees, though not when these photographs were taken last week, when it was cold and pouring with rain. The dazzling display of flowers did brighten up a dismal day, though.

Plant Public Enemy no.1

Japanese knotweed Fallopia japonica tops the table of alien, introduced plants that have become invasive weeds in Britain. Its phenomenal capacity to spread via deep, tough underground rhizomes and its resistance to herbicides, coupled with its tendencies to undermine building foundations, footpaths and roads, have created thriving businesses that specialise in trying to keep it under control. Introducing the plant into the wild is an offence and although it's not illegal to cultivate it in a garden, disposing of it when it begins to overwhelm your plot is a major problem, as Japanese knotweed-contaminated soil is classified as controlled waste and has to be removed by specialist companies. In the past much of the spread of the plant has probably been due to gardeners dumping plant waste, beside roads, rivers and canals. The fact that mortgage lenders are now refusing to lend to buyers of houses with Japanese knotweed in their garden should be sufficient deterrent for anyone contemplating planting it in their plot.

Since our Victorian ancestors first introduced it into their landscaped gardens it has spread around the country via fragments of rhizome in soil, especially in urban waste ground where it often forms four metre tall forests. Apparently, 137,500 tonnes of contaminated soil had to be removed from the London Olympics site alone, before construction could begin and, nationwide, about £150 million is spent every year trying to  control Japanese knotweed. One ray of hope for those seeking to bring it under biological control is that trials of a plant psyllid bug called Aphalara itadori, recently approved for release into infested areas, indicate that this insect could weaken the plant and make other forms of control, like herbicides, more effective

So, with all its destructive tendencies, is there anything positive to say about this aggressive invader? Well - excuse me while I reach for my flak jacket - there is. It's a magnet for honeybees. This fine specimen, that I photographed last weekend growing beside a pavement in Newcastle, near the Ouseburn, was humming with them. It's an ill wind, etc., etc.................