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This time of year, as we near the end of August, is in Ireland the season of seeds and berries. The trees and bushes are bearing berries and nuts in a plan to disperse their seeds a fair distance away.
Dispersal is a strategy, an evolutionary bet for survival of the species, spreading its chance against local disasters of flood, fire, pest and disease.
Also, it is not generally healthy for the seeds to germinate too near the parent plant, where penetrating sunlight will be poor and roots sucking the soil nutrients. Dispersal is the survival plan for many animals too, including humans.
Seeds may be dispersed by water, fire or they may hitch-hike on animals, stow away in human transport. But some parents entrust their young to the winds; some of those are blowing past us now.
Even in the city, the seeds of the lime trees crunch underfoot and the thistledown float gently past.
Lime trees (Linden, not the Citrus bearers of the lime fruit) are common enough in Ireland, even in cities like Dublin. Earlier in the year, they produced a faint scent from small nearly unrecognisable blossoms but which functioned the same way, to attract pollen-collecting insects.
The flowers are hermaphrodite, i.e both male and female but are not self-fertilising, so that insect pollination, particularly by bees, is necessary. Honey made from lime tree flowers has a distinctive taste but is somewhat restricted to where the source is available in large enough numbers.
Once fertilised, the tiny flowers begin to produce groups of two or more seeds on stalks. This time of year, they have ripened and come away, attached to a single specialised leaf as a sail.
They float and twirl in wind, whether falling from the tree or when thrown up by gusts from the leaf litter in the woods, on the roadside, etc.
They will lie dormant during the winter and sometime in the following Spring, some will germinate and begin the long struggle to grow into a tree.
The wood of lime is soft, light, fine in texture and resists splitting. Easy to work, it is used in turnery, carving, furniture; its resistance to warping makes it useful for construction of sounding boards and piano-keys.
Meanwhile this month, the thistles that flowered earlier are converting flowers to cotton down, billowing into a globe parachute ready to carry a single seed. They float leisurely through the air or are swept along by breezes and updrafts or tumble along the ground – before detaching the seed.
Thistles are not generally highly regarded but are important for many insects and therefore for many species of bird — and ultimately for us too.
I also observed years ago on an allotment I managed that young thistles could be pulled from the ground and the white stem eaten, crisp and faintly tart but not unpleasantly-tasting.
Many plants use the wind for seed and even pollen-dispersal, from grasses to flowering plants, shrubs and trees.
Ferns also send their spores on the winds, as do many fungi, including when in algae partnership to create lichens.
However only some species have developed the parachute – for example dandelions, thistles and groundsel/ ragwort – and only some trees grow wind-catching wings attached to or enveloping the seed, such as do the lime tree, sycamore and pine.
Obviously, this dispersal by wind is a hit-and-miss strategy – seeds may fall on stone, in river, lake or sea, where no growth for them is possible. To compensate for the wide number of unhelpful possibilities, each individual plant produces hundreds and thousands of potential offspring.
For higher mammals, that invest large sections of their lives in raising young1 before they are ready to disperse, the numbers of offspring per parents must be kept low, allowing for focus and concentration in care, defence and education/ training.
However, it is healthy for some of our human young to disperse too, though that should be a choice, not forced by war, disease, persecution, economic hardship or environmental destruction.
Certainly in the case of mammals, a wide gene-pool is good survival strategy – as long as we have a healthy world in which to spread.
1For humans, typically between a third to a fifth or their lives; for elephants about a third of the females’ lives, chimpanzees about a quarter. Rodents tend to opt for frequent litter of numerous offspring but their lives are short. Cats and Canines tend to have small litters unless pack or pride animals, when normally the alpha pair only breed and some of each litter become part of the pack as they grow (domestic dogs are not part of this natural scheme).
The typical lime tree in Ireland: https://futureforests.ie/products/tilia-cordata
Thistle in Ireland: https://irelandswildlife.com/jinny-go/#:~:text=There%20are%20several%20species%20of,found%20it%20in%20disused%20quarries.
Carline Thistle: https://www.irishwildflowers.ie/pages/442a.html