Live-bearing plants

there are alternatives to producing seeds

On one of many dribbly days in July, as I wandered along a beach on North Douglas, I noticed a little plant with white flowers. It’s called alpine bistort, but at our latitude it also lives in meadows and roadsides at lower elevations. The top of the flowering spike bore small flowers but on the lower part of the spike, where flowers normally develop, there were–not seed capsules or fruits–but small plants.

Photo by Bob Armstrong

This is an unusual plant because it does not usually produce seeds. Instead, each flower makes a bulb-like structure, and from this grows a tiny little plant. Eventually, the new plantlet falls off and lands on the ground, ready to grow.

Botanists call this habit ‘vivipary’, which means live-bearing or bringing forth live young. The scientific name of the plant (Polygonum viviparum) reflects this habit. The little green plantlet has already started to make its own carbohydrates, so in a sense, it is off to a running start when it lands in a suitable spot nearby. In contrast, a seed might wait until next year, or next decade, before it germinates and produces a seedling.

Calling this habit ‘live-bearing’ does not imply that any seeds produced in the more customary way are dead! Seeds are not dead at all. However, being encased in several layers of tissue gives seeds several options not open to these viviparous plantlets. Seeds can go dormant, in some cases for tens or hundreds of years, awaiting the right conditions for germination. The coverings of a seed may be modified in many ways (wings, sticky coatings, prickly surfaces, edible fruits) that give seeds a variety of ways to be transported to new sites, often at some distance from the parent plant. Thus, seeds can often disperse in time (dormancy) and space, but terrestrial viviparous plantlets often cannot. Moreover, seeds of most plants (but not orchids) contain stored carbohydrates packed into the seed by the mother plant, so they can draw on this stored energy when they germinate and start to grow. Viviparous plantlets do it for themselves.

There aren’t many native viviparous plants in our area. In addition to alpine bistort, we have a couple of grasses that are at least sometimes viviparous and the uncommon snow saxifrage. These species (and some others that live elsewhere) form their plantlets asexually—without pollination and fertilization, so each little plant is like its mother. Asexual vivipary is thought to occur most frequently where suitable terrestrial habitats are very patchy or where favorable seasons for germination and early growth are short.

So these plants have been reported mostly from arctic, alpine, or very arid areas.

Elsewhere in the world, however, some viviparous species produce plantlets by sexual reproduction. The flowers are pollinated and seeds develop, but the embryos begin to grow and, in some cases, plantlets sprout while the seed is still on the mother plant. In these species, there is regular genetic mixing across generations and offspring are not virtually identical to their parents. Many of these species live in warm tropical waters. Perhaps the most famous examples are some mangroves, whose fertilized seeds germinate while still on the parent; the whole young plant then drops off and floats to a new site.

Vivipary has evolved many times in the plant kingdom. Although the conditions that might favor the evolution of vivipary have been discussed by botanists, perhaps the only fairly clear conclusion is that different conditions are probably relevant for different species. As so often happens, there emerges no single, simple explanation.


Gustavus meadows

orchids, moonworts, and a plant that gives “live birth”

I recently visited Gustavus for a few days, so I had a chance to do a little exploring on a landscape very different from that of Juneau. After watching, from the convenience of the front deck of the cabin, all the young cedar waxwings (four of ‘em!), song sparrows, tree swallows, robins, hummers, and even two very new, tiny spotted sandpipers in the garden, plus a nest full of barn swallows almost ready to fledge, we set out to poke around in some of the wet meadows that lie on the forelands.

These long, narrow meadows probably occupy old stream beds that crossed the glacial outwash plain before the glaciers retreated to the upper reaches of Glacier Bay. The meadows are now surrounded by young spruce forest, where the mossy forest floor supports thousands upon thousands of twayblade orchids.

The meadows held odd assortments of plants. Nagoonberry and strawberry plants grew abundantly, side by side, with columbine and baneberry and soapberry mixed in, here and there. The plant known as sticky false asphodel was more common than in any other place I’ve explored. Ladyslipper orchids had finished flowering but were developing ripe fruits, and ladies-tresses orchids were in prime bloom. We found a weird fern that is related to the moonworts, which were reputed to have a variety of supernatural powers; among other things, they could make you invisible and unlock doors! These kinds of ferns bear all the spores on one shoot, not on the fronds like typical ferns.

Moonwort. Photo by Pam Bergeson

The small plant known as alpine bistort is not restricted to alpine areas, apparently, but the specimens here were considerably large than those I’ve seen on Mt Roberts. This little plant is distinguished by being ‘viviparous’, meaning that it produces ‘living’ young, as opposed to seeds or eggs. The lower flowers on the stem produce bulblets, which are capable of sprouting while still on the mother plant. When they drop from the mother plant, the young plants will be just like the mother, genetically, unlike offspring coming from seeds. A very unusual habit, which makes me wonder why it does so.

As we wandered along, we were roundly scolded by a greater yellowlegs, perched on top of the shore pines; it probably had a nest or chicks nearby. Moose had browsed the highbush cranberry bushes and perhaps a porcupine had nibbled the dwarf fireweeds. Sticklebacks darted about in a rivulet. And we found an abandoned winter nest of a vole, nestled on top of the moss; of course it was blanketed in snow in the winter.

Perhaps the most captivating find was a good population of long-leaf sundews, which are far less common than the round-leaf species. The round-leafs can be found by the millions in many meadows and muskegs, but the long-leafs tend to be concentrated on relatively barren ground, often near a pond, and are much less widely distributed. The fascinating thing was that the long-leafs had captured lots of insect prey on their sticky leaves, and the leaves were folded over as the successful captors digested the prey. In contrast, most of the round-leafs held no insects. Now why would that be so?

Some other sightings of interest: in the young spruce forest near the meadows, there was one very large hemlock tree, which must have got started before the smaller spruces. Usually hemlocks come in after the spruces, which favor mineral soils for germination and establishment. A big old hemlock amid all the young spruces was unusual. In another place, way down toward the beach where alders and tiny spruces have moved in, we found a single birch tree, a bit lonely in a stand of alders. It seemed very out of place there. If only it could tell us its story!

Just inside the edge of the forest, we found a yellow slime mold, with a brown slug wedged into one side. I presumed that the slug was eating the slime mold, and not vice versa—but who could tell?

That’s just a sample of things we found on our little voyage of discovery. As always, there were many observations of interest to curious naturalists, and our little explorations are always rewarding.