Sometimes Flowers are Jerks Part 2: Jack-in-the-Pulpit - Arisaema triphyllum - Petit prêcheur

Another plant currently in bloom is Arisaema triphyllum (jack-in-the-pulpit), a rather intriguing-looking plant with large three-lobed leaves and unusually shaped flowers.

Arisaema triphyllum

This species is native to eastern North America (range maps: North America, Canada). This plant has no protected status listings in the US [1] and is listed as secure in its Canadian range, except in Manitoba where it may be at risk [2].

Arisaema triphyllum

The flower of this plant tends to attract a lot of interest and attention because of its unusual shape. These two structures are called the spathe (the striped, green-purple hood section) and the spadix (the cylinder in the centre). The spadix is actually the inflorescence (structure to which the flowers are attached); the flowers are hidden inside the spathe.

Arisaema triphyllum spathe & spadix

Why would a plant be shaped this way, carefully shielding and reducing access to its flowers? Wouldn't that reduce pollination?

Well, certainly that would be the case if the plant were wind-pollinated. Or if it were pollinated by larger animals eg bats.

But A. triphyllum is pollinated by fungus gnats [3]*. And this plant is a giant jerk about it.

The plant is visited by fungus gnats, which crawl on in to get access to the flowers. But then once they're inside, the size and shape of the hood make it seem totally closed [4]; the flies have a hard time getting out. The male flowers, which have some interest in the pollinator escaping, have a small hole at the bottom of the spathe through which pollinators can escape (after brushing past all the male flowers on the way down) [4]. The females have no such hole, so pollinators are more likely to die in there [4]. But while they're stuck in there they fly around and thrash and generally get themselves coated in pollen, or in the case of the female flowers, coat the pistils with the pollen they've already collected.

So this flower traps its pollinators to increase its odds of successful pollen transfer, and with the female flowers has a high chance of killing the pollinator outright. Harsh.

Other plants do this, of course, with varying degrees of harm. For example, in yesterday's post I talked about Cypripedium acaule, which also traps its pollinators (but it always lets them out!). C. acaule has a one-way hole in the front of the flower through which pollinators enter, and then a sort of pollination-tunnel through which they can exit up around the top of the flower [5]. First, the pollinator is forced to rub past the pistil, which ensures that if they're carrying pollen it's transferred over [5]. Next, they get brushed with a ton of little pollen-covered hairs, ensuring that the pollinator leaves with plenty of pollen for the next flower [5].

Cypripedium parviflorum and Cypripedium arietinum are both also pollinator trappers (sometimes referred to as kidnapping).

Trapping helps to increase the odds of successful pollination when a pollinator does come by, by increasing the odds that pollen will be deposited on the pistil.

A. triphyllum is often considered dioecious [6]; bisexual flowers have been noted but whether these flowers reproduce bisexually is debated [7]. An interesting aspect of this species' gender segregation is that it is not fixed by generation; a given individual can vary its sex from year to year; this sex variation is generally thought to be linked to the size/age (available stored resources in the roots) of the plant [3,4,6,8]. The general idea is that female function (production of fruit and seeds) takes more energy than male function (production of pollen), so a plant with more available resources in its roots, eg one which is larger or one which was able to store more energy the previous year (which would be more possible if it was male the previous year), is more likely to be female for the season.

I did manage to get a photo of a unisexual female, showing the flowers at the bottom of the spathe. I apologize for the poor image quality, I was in a hurry.

Female flowers of Arisaema triphyllum

As you can see, this flower has very plain flowers, just a little fruiting bulb (an ovary) with a pistil on the tip (the white part). Given that their visual characteristics are not related to attracting pollinators, it is no surprise that the flowers are unremarkable to look at; resources are redirected to more valuable functions such as producing fruit.

*there is debate and disagreement about this [4]

Sometimes Flowers are Jerks Part 1: Pink Ladyslipper - Cypripedium acaule - Sabot de la vierge

The Orchidaceae (orchid family) have started to bloom now. My father and brother have reported that the Cypripedium arietinum (ram's head orchid) and the Cypripedium parviflorum (yellow ladyslipper) are both blooming now on my parents' property in the upper Gatineau. I wrote a blog post about those species last year. This year, my father and brother also reported something special.

While wandering around, they found another orchid, this one quite unusual for the area: the pink ladyslipper (pink lady's slipper, moccasin flower). The species is relatively abundant in Canada but occurs more in pine forests rather than deciduous (or mixed deciduous like is found on my parents' property). They were kind enough to send me photographs so that I could write a blog post about them, so today's photos were taken by guest photographers!

Cypripedium acaule with leaves - note the paired basal leaves and the lack of leaves on the stalk

This lovely flower is native to eastern North America (NA range map here; Canadian range map here). Unfortunately this plant is endangered in Tennessee (also commercially exploited in this state) and Illinois, exploitably vulnerable in New York, and unusual in Georgia [1]. In Canada it is doing better, listed as secure for the country as a whole and in most of its range; it is sensitive in Alberta, and has an undetermined status in the Northwest Territories [2].

Cypripedium acaule front view

So why do I call this pretty flower a jerk? Well, this is a 'deceptive' flower. Specifically, this is a food-deceptive flower. This species (along with both C. parviflorum [3] and C. arietinum [4]) has a strong fragrance which it uses to attract pollinators who associate the fragrance with nectar rewards -- but the plant doesn't produce any nectar at all, so the pollinator gains no benefit for its visit [5]. One might wonder why a plant would evolve such a system, of course; these plants are pollinated much less frequently than reward-offering plants [6,7,8], and not producing nectar would not necessarily constitute a particularly large energy savings [8]. The question of why deception is such a common strategy in orchids is an interesting one for researchers as a consequence. A number of theories have been proposed, some of which are discussed here for those interested.

Cypripedium acaule side view

One of the natural consequences of the plant's deception is that it depends on naive bees (bees that haven't visited it much before) for pollination, because they learn after a few tries that the flower doesn't have any reward and stop visiting [5,6]. So, there are few fruit produced each year (few successfully pollinated flowers) [5].

Cypripedium acaule front view - close - note the fine hairs (trichomes) on the petals and sepals

There is another interesting aspect of this (and other orchids') reproductive ecology that I will discuss in conjunction with some other flowers later this week, so those who are aware of the interesting thing I am skipping over -- I know, I'm just saving it for another post.

Cypripedium acaule bottom view

Many of these orchids are rare, and tend to do very poorly when transplanted in gardens. One of the major reasons for this is that many orchids are reliant on a particular type of fungus in order to germinate seeds [5,6], so they can't reproduce outside of areas where the fungus is present; so, when gardeners dig the flowers up and bring them to their gardens, the plants will not survive or reproduce effectively [6]. Thus, if you find these species in the wild please do not give in to the temptation to take the flowers. They won't survive and you will damage the population's genetic diversity. In fact, it is illegal to remove the pink ladyslipper in Georgia (poaching) [6], as this is becoming a serious threat to a variety of orchid populations. This caution applies to most wild orchids including the yellow ladyslipper and the ram's head orchid.

Many thanks to my guest photographers for the gorgeous shots!