Spring in the City: First growth - Seeing past the snowdrops

There’s so much more to spring than snowdrops, daffodils and bluebells. While flowers with bulbs and corms do have the advantage of stored energy to fuel their growth, catkins are already dancing, tree leafbuds are swelling and pavement and treepit plants are flowering. Armed only a little time and perhaps a hand lens there’s lots to see in spring, even in a city.

One of the benefits of city botanizing is the wide range of native plants and naturalised introductions which are thoroughly monitored by urban plant spotters. London is also an ‘urban heat island’ with higher temperatures than surrounding countryside because of the different way hard surfaces retain the sun’s heat. This additional heat can be problematic, for example making summer heatwaves more likely, but there’s a positive impact of warmer winter temperatures on plant flowering.  On a grey New Year’s Day this year I counted 33 wild and naturalised plants in flower along the Southwark section of the Thames Path. Highlights for me were gallant-soldier (from Peru), narrow-leaved ragwort (from southern Africa) and once rare Jersey cudweed. 

Despite that score of 33, it’s presumably stating the obvious to say that most native plants don’t flower during winter. Other than a few honey-bees and the odd queen bumblebee visiting snowdrops on warmer days, there’s little on the wing in winter or very early spring. For plants determined to get down to sexual reproduction early in the season, wind pollination is the only option.  The strategy for some of our native trees is to produce wind-pollinated flowers well before leaves. Wind pollination is costly requiring huge volumes of pollen to successfully reach the flowers of other trees of the same species. It’s risky enough relying on the right sort of spring wind without having leaves getting in the way of successful fertilisation.

Some wind-pollinated trees, like hazel, alder and pendunculate oak, are monoecious which means they have male and female flowers on the same tree. They are also self-incompatible; in other words a tree can’t fertilise itself and pollen does need to reach the female flowers of other individuals of the species to produce viable seeds. Powdery yellow hazel catkins and its tiny female flowers exploding with crimson styles are the first of these to appear and were visible in Sydenham Hill Wood in January this year. Others like grey and goat willow are dioecious, with individual trees having either male or female flowers but not both. The willows are later than hazel but usually flowering by March.

Most insect-pollinated plants have the male stamens and female stigma as part of a single flower structure so that the insect collects and deposits pollen at the same time. For wind-pollinated trees like hazel, the male and female flowers or inflorescences can be quite spaced out (unlike the ones shown in my photo here). Both sexes of flowers need to be positioned to optimise either pollen scatter or collection but they don’t need to develop right on top of each other. Pollination strategies affect the characteristics of pollen grains too. Pollen from insect-pollinated flowers is often sticky to enable it to attach successfully to the pollinating animal. Wind-pollinated pollen grains are relatively smooth which means they are less likely to get attached to a surface other than the sticky female styles waiting hopefully for them.

As well as a reminder of different pollination strategies and trade-offs, early spring is a great time to revel in the new leaf buds. Every year I find myself marvelling at the amazing palette of different greens from the parakeet-green of hawthorn to the chartreuse of hornbeam leaves. Meanwhile the velvety black leaf buds of ash stay resolutely dormant, one of the very last trees to come into leaf.

The trees’ leafless branches benefit plants on the woodland floor too. Among the fleshy bluebell spikes and patches of feathery cow parsley, some less showy plants are taking advantage of the glimpses of spring sun. Garlic mustard, softly hairy dog’s-mercury and wood anemone are all satisfyingly easy to recognise.

New grass growth is visible too. Where there’s more light, the characteristically flattened new shoots of cock's-foot are pushing up through last year’s browning tussock in a woodland glade and annual meadow-grass seedlings sprawl on the edge of paths. On a fallen tree, a legion of tiny sporophytes of capillary thread-moss stand to attention, poised to invade a new patch of bark.

There’s so much more to spring than bulbs. Pavement pioneers, wind-pollinated flowers and other woodland plants can be very rewarding too.  There are times during the shortest days of winter when it is tempting to wish away our seasonal changes but what a sharp sweet relief the first growth of spring provides in all its forms. And the early spring plants in a seasonal environment like ours are a reminder of some fascinating evolutionary trade-offs in the plant world.

Note: As a botanist in learning I do my best to check plant identifications with more experienced botanists but take full responsibility for any remaining mistakes. I’m always delighted to receive corrections so please contact me with them via Twitter @suburbanwilduk