Saturday 15 December 2018

Undesirable alien Winter Heliotrope coming into flower

Winter Heliotrope flowers are strongly scented of vanilla
Winter Heliotrope flowers are strongly scented of vanilla

Jim Hurley - Nature Trail

Winter Heliotrope is an invasive alien. It is an alien in the sense that it is not native to Ireland; it is a blow-in from central Mediterranean climes especially southern Italy, Sicily, Sardinia and North Africa. It was introduced by Victorian gardeners for ground cover in damp areas.

Following its introduction, it proved highly successful, so successful that it escaped from the confines of gardens and started spreading itself around our green and pleasant land. It has been recorded growing in every county in Ireland and is believed to be still actively spreading.

It is invasive in the sense that wherever it grows it is inclined to take over, out-competing our native flora. Everyone must know of stretches of roadside verge completely clothed in the shiny, ground-hugging, heart-shaped leaves as big as horses' hooves.

It favours moist ground, so it does particularly well on damper soils where it forms large and very persistent stands. It is a difficult weed to kill but broad-spectrum systemic herbicides like the popular and much-used glyphosate are very effective on fresh growth in springtime.

Some plants are both male and female in that both sexes are found in the one body; these plants are said to be monoecious. Winter Heliotrope is dioecious. Like humans, the plant comes in two different sexes; there are distinct male and female plants and, obviously, both must be present for the species to breed and produce seed.

The plants that Victorian gardeners introduced to Irish gardens and estates were all male. As far as is known, there are no female Winter Heliotropes in Ireland; the entire population is male. So, how are these males breeding on their own? The answer is that they aren't reproducing sexually; they are spreading asexually or vegetatively.

Winter Heliotrope spreads by underground creeping stems called rhizomes. They are literally creeping their way around Ireland. A digger driver working by a stand of plants may inadvertently pick up a fragment of rhizome on the bucket and aid the plant's dispersal by carrying the fertile fragment off to pastures new.

Since there is no genetic variation, the entire population of Winter Heliotropes in Ireland is composed of clones of the original imports. While it is an undesirable and ugly alien in the countryside its one saving grace is that it is one of the few plants coming into flower at present and its purple-tinged white flowers are strongly scented of vanilla.

Fingal Independent