FLAUNTING FLOWERS – AND FLIERS, SAILORS AND HITCHHIKERS

Diarmuid Breatnach

(Reading time: 3 mins)

          In a couple of previous posts I remarked that plants have developed amazing innovations in order to grow, adapt to conditions, colonise strange ground and to propagate their species. I commented also that their variety of methods outnumbered those of our section of life on Earth, the animals; this month of June is a good time to see some of them at work.

Along with all their other innovations, plants evolved some very impressive ones in procreation and in dispersing the next generation. Pollen, a fine powdery substance that is the equivalent of mammal sperm could be and was spread by the wind and plants developed early “flowers” like grass “heads” or catkins to catch the passing pollen. The development of the flower and blossom brought in a partnership with animal pollinators to greater efficiency. Attracted by nectar and to some extent pollen, insects and some birds visited male plants flaunting their flowers and unconsciously picked up pollen which they deposited at another flower they visited, thereby soon fertilising the female counterparts. And the plants developed different ways of dispersing their offspring too.

Flowering plants, angiosperms, are now the overwhelming majority of plant type on Earth not only in variety but in total bio-mass – but they are latecomers in the evolution of plants. Once arrived, in order to attract pollinators, flowers produced nectar and were developed in a huge variety of shapes (some we would not even normally describe as flowers) and colour.

Probably smell came later. Some botanists speculate that scent was first used by some plants to discourage insects and grazers which, if true, is amazing enough. To then go on to develop scent to attract pollinators is a leap that staggers the imagination. Flowers and blossoms using smell are particularly noticeable at dusk and night, a time of low visibility for flowers, when presumably they are visited by moths.

A hive honey-been, one of the most common pollinators, approaching a flower (perhaps a dandelion’s) intending to collect nectar and perhaps pollen but will certainly collect the latter inadvertently. Note the collection bag on its legs. (Photo source: Internet)

Early plants did not have seeds or flowers (some still don’t) so the whole paraphernalia around them had to be developed from other existing parts with originally completely different functions, an impressive feat of adaptive engineering (some of us could convert a bicycle, a machine for locomotion, into an electric power generator but still ….).

The petal seems to have been the key development which spurred huge flower diversity to outcompete others in attracting pollinators and it is known now that some carry identifying patterns in ultraviolet, invisible to us but advertising like neon lights to bees. Some, like the dandelion, group many single-petal florets together to make what appears to us as one flower, each floret capable of individual survival.

USING OTHERS TO SPREAD THE SPECIES

Just behind the flowers of many species is a little node which when fertilised begins to swell and form a fruit, with the developing seeds inside — or single seed in the case of some species, the Prunus plum family, for example. This is another amazing trick of the plant – it has produced attractive fruits, full of sugars when ripe, to attract animals (such as ourselves) to pick them and either discard the seeds as we eat the fruit or pass them through our gut to be deposited on earth — along with a handy dollop of manure.

On the grassy plains of the South American Pampas there are isolated copses of trees whose occurrence seems mysterious. An investigating botanist concluded that horses were eating the nuts of the parent trees some distance away then, as they travelled across the plains, at some point defecated with some intact nuts among their faeces resulting in some years later – a grove of trees. Of course horses (or their riders) might also seek the groves out for shade and, while there, drop a few more nuts. Horses have only been in the Pampas for a few centuries and probably the other local grazers are not overly-fond of saplings (or not of those tree species).

Nuts and seeds are also stored in different caches by some mammals and birds, for example here in Ireland by squirrels and magpies. They don’t always dig up all the stores later – perhaps they forget where some of them are – and in the spring, those nuts become saplings.

Well enough. But producing fruit and nuts is a lot of work and depends on the assistance of animals, especially mammals and birds, for dispersal.

WIND-SAILERS AND BOMBARDIERS

Immature lime tree seeds with their “kite”, Drumcondra roadside, June 2021. (Photo: D.Breatnach)
Seed-carrying parachute downy ball of the Meadow Salsify (I’m guessing) Dublin Botanic Gardens, June 2021. (Photo: D.Breatnach)

Some plants scorn to use animal helpers to disperse their young and instead employ the wind. Dandelions, thistles and many other plants send their seeds off on downy parachutes, often to land kilometres away. And some of those wind-sailers are tiny seeds of very large trees, like poplars and cottonwoods, using cotton tufts to carry their offspring off into the world, which is happening right now in June in Ireland. Some, like the sycamore, grow “wings” on their seeds which, when dry in the autumn and winter, spin away on the wind; not only that but when they strike mud they are sometimes twisted by the wind on their “wing” to ‘screw’ the seed into the soil.

The catkins of a poplar in June 2021 on Tolka banks as the river flows through Griffiths Park, north Dublin city; tufts of cotton carrying tiny seeds float away this time of year. (Photo: D.Breatnach)

Many plants with pods, for example the legumes, will have their pods crack open when dry to “spill the beans” upon the soil, or some might shake loose and fall as the rest are eaten by birds and mammals. That is all a bit pedestrian for the gorse or furze, the pods of which explode on a summer’s day, shooting the seeds away. One such afternoon I sat among gorse bushes on Killiney Hill and was startled to hear what sounded like a weak pistol shot. Then another …. and another …. and all around me the bushes were shooting out their seeds, the lucky ones to create new bushlets (yes, I did just make up that word) the following year.

HITCHHIKERS

With fruit and nuts we saw plant offspring being cached or stowing away inside birds and mammals. But some hitch-hike on the outside too, like the burs that work their way into animal fur and into our woollen clothing. These are seed cases covered in tiny hooks, said to have been the inspiration for the invention of velcro fastenings in fabrics. The cleaver or “sticky-back” may attach many of its small burs to a passing mammal, while the burdock, with its much larger burs, is more likely to hitch a ride in ones or twos. Tiny seeds of many grasses stick to wool, fur and hair too, especially when damp, as we learn when we walk through meadows in late summer or autumn. But many other grasses with larger seeds, including cereals, grow “ears” with spikes attached to each seed and these too, when dry and ready to go, get picked up by the wool or fur of passing traffic.

All aspects of the Cleaver plant (“Stickyback”), another hitchhiker for its seeds. (Photo source: Wikipedia)
Hitchhiker seeds — the ‘fruits’ of the burdock after flowering become a bur to attach to passing traffic. (Photo source: Internet)

At some point in the future, these clingers will be brushed off or fall away, ready to sprout, if conditions favour them, in their new home.

Even the hot winds of forest fires are used by some conifers (which are of the non-flowering gymnosperms) to spread seeds from inside their cones – each seed has a little vane around it to help it sail the wind. Sure, many will burn before they sail or blow into another fire – but some will survive. The alternative is just to burn.

SURFERS

The coconut, on the other hand, floats its fruit to distant shores – it was not for tourist brochures that the palms grew fringing tropical beaches. Falling coconuts roll away from the tree too – if they don’t hit some unfortunate large animal first (bouncing and rolling of heavier seeds, though not normally described as a seed dispersal method, clearly plays a role).

Many other plants use floods to populate different areas, often creating stronger banks or islands as their offspring grow, sometimes even changing the very course of a river or stream. The various willows and alders are adepts at this, as are many kinds of reeds and rushes.

UNDERGROUND EXPANSION

Floating colonisation is carried out by some seeds but there are other surfing colonisers too: severed branches or leaves that grow roots into water, uprooted saplings, tubers and bulbs. Bulbs, rhizomes and strings of tubers have been used by many plants to store food for offspring, nascent new plants hiding below or on the ground. Even when a field of potatoes is harvested, there are often tiny potatoes remaining that escaped the harvesting procedure – the following year, they may be seen, sprouting new plants.

An unusually solitary Yellow Flag Iris on Tolka banks as it flows through Griffiths Park, north Dublin city in June 2021 (they can be seen in clumps along the nearby Royal Canal). The Yellow Flag uses both seeds — fertilised by pollinators in the flower — and underground rhizomes to propagate the species. (Photo: D.Breatnach)

RUNNERS

A somewhat similar method to strings of tubers – and possibly their actual origin – is the underground runner, like a root running just below and parallel to the surface, sending out shoots upwards and roots downwards at intervals, each of those becoming a new plant, a clone. Many grasses employ this procedure, some bunching close like the bamboo and others spreading away in different directions, as for example with the couch or scutch grass. The latter may be to the despair of the gardener, who however will use strawberry overground runners to grow new fruiting plants.

Grasses are an evolutionary late and special kind of plant that can be grazed down to ground level and grow again, year after year and as we saw earlier, wind and hitchhiking are their special seed dispersers. Grass provided a renewable food source for animals that could convert its leaves, stems and seeds into sufficient energy – enter herds of goat and sheep, horse, donkey, zebra, deer, antelope, bison and cattle! And therefore enter their predators too, in particular the big cats, canines and – homo sapiens.

She in turn would domesticate some of those species, including another predator as helper, the canine. That combination would change the world quite significantly and when homo sapiens learned to cultivate some of the grasses for their seeds, i.e cereals, well ……!

Some plants are capable of employing all of the various methods of reproduction and distribution: seed, tuber, branch or leaf regeneration. Plants are the innovators par excellence of visible life on Earth.

Some plants are capable of employing all of the various methods of reproduction and distribution: seed, tuber, branch or leaf regeneration. Plants are the innovators par excellence of visible life on Earth.

End.

Stray immature barley (maybe) seed heads, Drumcondra roadside, June 2021. Cereals such as these use hitchhiking inside grazers as well as hitchhiking by snagging passing wool and fur with spikes on the “ears” (Photo: D.Breatnach)

A mixed group of seed-spreaders: wind parachutes (dandelion or salsify maybe), pod-rupture (red clover), hitchhikers and wind-sailers (grasses), (scatter by movement and wind) broad-leaf plantain and one of the umbellifers, probably cow parsley (by the leaves). Drumcondra uncultivated garden, June 2021. (Photo: D.Breatnach)

SOURCES

Flower production:http://www.bbc.com/earth/story/20141017-how-flowers-conquered-the-world

https://en.wikipedia.org/wiki/Flowering_plant#Reproduction

https://www.nationalgeographic.com/science/article/big-bloom

Pollination by bees and what they see: https://www.beeculture.com/bees-see-matters/

Seed dispersal methods: https://www.sciencelearn.org.nz/resources/103-seed-dispersal

https://www.britannica.com/list/falling-far-from-the-tree-7-brilliant-ways-seeds-and-fruits-are-dispersed

Identification: https://www.teagasc.ie/media/website/crops/horticulture/vegetables/Illustrated_Guide_to_Horticultural_Weeds_2020.pdf

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