What's in a Name - "Wild Strawberries" and Scientific Nomenclature - Fragaria vesca

By now you will have noticed that I refer to plants on this blog primarily by their scientific names. I will usually supply one or a number of common names as well, but I will write about the plants by their scientific names.

There is good reason for that, one of which I have an opportunity to exemplify today.

So I have posted recently about wild strawberries (once or twice), and now I want to post about wild strawberries again. But this time I'm talking about a different species entirely: Fragaria vesca (wild strawberry, wood strawberry, alpine strawberry).

These are not the only species referred to by the name "wild strawberry", either. This is a frequent issue with common names. Simply put, if I were to write about a plant using the common  name, I would end up quite imprecise. Using the species name cuts down on the confusion and debate about which species I am referring to.

Another issue is that many of the more familiar species have a wide variety of names which are used variously frequently. This leads to some confusion about plant identification and often debate about the correct name for a given species. I avoid this issue altogether simply by using the accepted scientific name for the plant in question. 

One more serious issue I have with the use of common names for plants is that a large number of species simply do not have common names at all. This is especially true with insects and small plants.

Fragaria vesca leaves

So the species I'm going to be talking about today, Fragaria vesca is native to most of the North American continent [1]. Fragaria vesca subsp. americana is extirpated in Indiana [2] and otherwise unlisted in the US. In Canada, Fragaria vesca is listed as secure in most of its range, except in the Northwest Territories where its status is undetermined, and in Newfoundland and Labrador, where it has not been assessed [3].

The fruit and leaves of Fragaria vesca are a source of food for the Portola woodrat and valley quail [4], and is available in some nurseries as a garden plant [4].

Fragaria vesca, like Fragaria virginiana, is a member of the Rosaceae (rose family) which produces an edible red berry. The fruit of Fragaria vesca, however, is differently shaped, with the seeds riding on the surface of the fruit (none of the indentation which is visible with Fragaria virginiana) and often a more pointed shape. 

Fragaria vesca - more pointed shape, seeds riding on the surface

In comparison, the seeds on Fragaria virginiana are inset in the fruit:

Fragaria virginiana - fruit with seeds inset

The fruit is also displayed on a stem which rises above the leaves in Fragaria vesca, while the fruit is generally below the leaves in Fragaria virginiana.

Fragaria vesca fruit - above the leaves

Note that the fruit in Fragaria virginiana, by comparison, is below the leaves:

Fragaria virginiana - note the fruit below the leaves

Although I do pick and eat Fragaria vesca, I don't go so much out of my way for it, because it is not so tasty as Fragaria virginiana. It's palatable enough, but where Fragaria virginiana is sweet, juicy, tart, and exceedingly flavourful, Fragaria vesca is blander. The distinctive characteristic which makes this fruit much less appealing to eat also makes it rather interesting, however: the fruit is quite dry, and for that reason it is exceptionally light. You can have a handful of them and they will not feel weighty at all in your palm. The fruit is large for its weight, likely due to its airy, somewhat foamy texture.

All told, Fragaria vesca is tasty enough, but I wouldn't go far out of my way for it. I do harvest them when they're available, though. I got a nice handful today:

Fragaria vesca - a respectable harvest for a few minutes' work

Gynodioecy and the Wild Strawberry - Fragaria virginiana - Fraisier sauvage

So, why will I talk about gynodioecy today? Well, I noticed that Fragaria virginiana (wild strawberry) is blooming! F. virginiana is a gynodioecious species, so I thought I might try my hand at explaining why this plant is of so much interest to scientists. Gynodioecious species like this one help us to investigate questions about the evolution of separate sexes (among other things). Definitions, explanations, and much more below, after my usual more basic commentary about this lovely species.

Fragaria virginiana in bloom

This species is very widely distributed, native to all parts of North America (range map here). It is not at risk anywhere in its US range [1] (and, in fact, is considered a weed in some parts of its US range for its ability to spread prodigiously [1]), and is secure in all parts of its Canadian range except Nunavut, where it is sensitive [2].

This plant produces a fruit which is edible (and delicious!), and is one of the two species which was used to breed Fragaria x ananassa (commercial strawberries) -- the other species being the Fragaria chiloensis (coastal strawberry) [3,4,5].

Fragaria virginiana flower

F. virginiana grows primarily in meadows and open spaces [3,5,6] and will also reproduce via vegetative propagation (not just sexual reproduction!) [3,5,7,8].

Now hold onto your hats, ladies and gentlemen, we're going to talk about the evolution of separate sexes!

In animals, dioecy (separate male and female individuals for sexual reproduction) is the norm. In plants, however, dioecy is relatively uncommon, with only roughly 6% of known species of angiosperm (flowering plants) having separate sexes [9]. The primordial state for angiosperms (flowering plants) is monoecy, where both male and female gametes are produced by any given individual (hermaphroditism). So this raises the question of what evolutionary path has led from hermaphroditism to dioecy.

There are a number of proposed avenues for the evolution of dioecy. I'm only going to talk about one of them today: gynodioecy. This pathway is the most commonly studied [9], likely because gynodioecy is relatively common in plants, with about 7% of known species being gynodioecious [9].

In a gynodioecious species, there are two types of flower: female flowers, and hermaphroditic ("perfect") flowers. The categorization of the flowers as female or hermaphroditic is based more on function than appearance. This is because the occurrence of this type of sex distribution begins with a deactivation of male fertility in some individuals [9,10] -- in other words, some of the individuals stop producing pollen or stop producing viable pollen but may still, at first, have the physical structures associated with pollen production (there are a number of possible ways that this can occur, but for today's post just the fact that it happens should suffice). At this point, we have two types of flowers: those which are functionally female (minimal or no male reproduction -- nobody's getting pollen from them), and those which are functionally hermaphroditic (their pollen fertilizes others, and they receive pollen from others).

So it's fairly intuitively obvious that the hermaphroditic individuals have a reproductive advantage in this kind of scenario: they get more chances to pass on their genes. To make this easier to understand, I've created a little table which should help to illustrate the situation. Let's take the theoretical reproductive opportunities for any given individual. That individual, if it produces fruit, has guaranteed that it gets to be the female parent of those seeds; and if it produces pollen, has the chance of also being the male parent of other seeds. The columns represent the two parents of any given fruit (female parent and male parent).

Table 1. Reproductive opportunities (parentage) for hermaphroditic plants

Table 2. Reproductive opportunities (parentage) for female plants

Basically, out of 4 reproductive opportunities, the hermaphrodite takes 2. 2/4 certainly isn't bad! Flowers that don't produce pollen, however, lose their chance to be the male parent of other fruit, as illustrated in Table 2. So these flowers only take 1/4 opportunities to pass on their genes.

So wait, you might say. Wouldn't that mean that plants that are female will be outpaced by hermaphrodites, and their genes will just eventually disappear?

That's would certainly be the case if it weren't for female compensation. Those plants which aren't producing pollen anymore see a rise in seed viability [9,10]. Basically, their female fertility is increased when their male fertility ends. This is probably because the energy that was originally being devoted to producing pollen can be redirected toward improving seed viability [9]. So the female individual actually is also coming out better in this system; she gets a better return on her investment for the fruit and seeds she produces, producing more viable offspring from her fruit than a hermaphrodite.

From this point on we get to theory, but the principle is that because there is less competition for male parentage (more chances to fertilize a female flower), and because it takes a lot of energy to produce fruit and seed, it will be more and more advantageous for the remaining hermaphrodite flowers to shift toward investing more energy in pollen and less energy in fruit [9,10]. This process would eventually lead to dioecy (separate sexes).