Plant Rarity (or, Plant of the Week part 1)

I was going to post about the plant I studied in school, and ended up with lots of things I could say about it (imagine that). So, I thought I would start with a bit about how I chose this rare-but-not-endangered endemic, and also how plants can be rare.

I found my study plant, Physaria bellii, or Bell's Twinpod, by visiting with the Colorado Natural Heritage Program's very competent botanists and giving them sort of a laundry list of what I wanted in a study system, and they were happy to oblige: I wanted the sites 2 hours or less from my home, I wanted to work with something that at the time of the conversation (September) still had vegetation showing so I could collect leaf samples for DNA, and if possible, something that was rare and hybridizing with a more common congener. But not too rare, as I didn't want to compromise the species by sampling it.

How about Physaria bellii? Okey dokey. Physaria bellii is named after the namer's colleague, which sometimes happens in science. The genus belongs in the Brassicaceae, or mustard family, and P. bellii is just one of several narrowly-distributed species of Physaria in Colorado. It is a habitat specialist, found mostly in soils from the Pierre and Niobrarra shale formations, which make up hogbacks running along the east side of the Front Range of Colorado from Denver north to WY. It will also sometimes be found in soils associated with red sandstone. The habitat is patchily distributed, and as a result, one might hypothesize there is limited gene flow.

In the process of studying this species, I came across a simple table by Deborah Rabinowitz, which is called the Seven Forms of Rarity. When you compare the various combinations of population size (large or small) and geographic range (broad or restricted), there are seven ways a plant species can be rare. You'll notice there's an eighth combination, but that's when the factors come together and the species isn't rare (large population size, broad geographic range).

Here's the table:

Physaria bellii comes in at the upper rightmost cell. It's locally abundant in its preferred habitat, but that habitat is rare, so it is as well. Notice how plants can be rare in a variety of ways, and of course this helps when trying to figure out how to conserve rare plants.

OK, a bit about the looks of this plant. As you can see from the picture, it's a low-growing plant, and has yellow flowers. Those flowers smell very nice, as I found out when I was growing them in the greenhouse to do crosses. I guess I had just never bent down close enough in the field to get the scent. They are pollinated by generalist pollinators, and can have 50-200 flowers open at one time. The flowers mature into the "twinpod", a two-part fruit that can have two seeds per side, but usually has one. The leaves are covered by tiny hairs, perhaps as a water-loss-prevention adaptation. The leaves are variable, but all spatulate with no sinuses, and this helps distinguish P. bellii from its relatives.

Next time - hybridization, population genetics and chromosome squashing.

Plant of the Week - Roses

Roses aren't quite the dogs of the botany world, but they still have displayed an enormous variety of scent, color and form. Roses are part of the Rosaceae, with over 100 genera and more than 3,000 species. The family is divided into four subfamilies, but whether these groups are well-supported by DNA sequence information is still under some debate. The family ranks up there with the grass (grains) and pea (soybeans) families as the some of the most economically important crops.

The family contains many well-known fruits such as apples, pears, cherries, strawberries, and peaches. They all share a common floral formula, with some of the floral parts (sepals, petals and stamens) fused into a structure called a hypanthium. This shows different arrangements of parts, if you are interested.

Cultivated roses are often bred to be double-flowered, that is they have more petals than their wild ancestors. This phenomenon is thought to arise from mutations that tell the stamens (of which there are many) to develop as petals, which is apparently a "default" structure when other information is lacking.

In terms of cultivated roses, there are Old Garden roses and Modern Garden roses. The Old Garden roses bloom once in a profusion of double-flowered, highly scented blooms, on shrubby, disease resistant plants that are white, red or pink. Modern Garden roses are the result of selection for specific traits, and as you would imagine, the variety is pretty impressive. Within the Modern Garden roses, there are other classifications, such as miniature, and climbing, as well as the more familiar shrub roses. By introducing genes from a wild relative, (Rosa foetida), Hybrid Tea rose breeders were able to develop varieties with shades of copper, deep yellow, even lavender. In an interesting turn of fate, these same beautiful colors also brought along decreased disease resistance and scentless blooms, so they are bred more for color and are considered higher maintenance than other varieties.

Floribunda and Grandiflora roses are popular these days, and combine the best traits of Hybrid Teas with heightened disease resistance and more of that yummy rose scent.

The cut flower industry depends on perfect-looking specimens that often come from far away. As a result, the industry has been perhaps too reliant on the application of pesticides, and you can read about it here and here. I'm not sure if it's marketing or the real deal, but it seems that roses from Ecuador are really popular. Perhaps due to climate and soil, the flowers can be huge! In a great example of the consumer wanting to do the right thing if given the opportunity, Whole Foods and Sam's Club now offer Fair Trade roses from Ecuador. This certification protects workers (mostly women) from excess pesticide exposure while paying them a fair wage; everyone seems to win in this one.

I have two roses bushes in my garden. One's a 10 foot monster that was a housewarming present when my x and I moved into our last house. I wasn't all that concerned about the implications, it was a free rose bush! It has yellow-orange blooms that smell divine and it is about as unfussy as garden plants can get. The other one is a climbing rose I bought last year to grow up the corner of my house and it's got single flowers that are white on the inside and deep purple at the outside. I'd plant more, but I don't have any more room!

Hypanthium image from here. Rose farm image from here. Peach rose image from here.

Plant of the week - Milkweeds (Asclepias)

I thought I'd start a feature where I could post some cool stuff about plants. Let's start with the milkweeds, in the genus Asclepias, and the namesake of the family Asclepiadaceae. There are 75 species of milkweed in the US, and the genus is distributed throughout. The common name comes from the milky sap, which contains several chemicals that are toxic to many herbivorous insects and can cause contact dermatitis if it gets on your skin.

Members of this genus are famous in that they are the sole food of the Monarch caterpillar (Danaus plexippus), which probably merits a post by itself, given its hefty migration. The caterpillars feed exclusively on the leaves of milkweed, and this confers toxicity to the individual through subsequent stages of its life cycle. I can remember learning about this in school and seeing a video clip of naive blue jays being offered monarchs, eating, vomiting, and then being offered a Viceroy butterfly, which is a mimic. Those savvy jays declined anything that looked like a monarch, thus showing us how mimicry works in nature.

The flowers are attractive to many pollinators, but this genus has an unusual pollination mechanism that favor certain sized pollinators. The flowers are unusual in appearance because they have an extra whorl of parts in addition to the usual four (sepals, petals, stamen, pistil) called the corona. Here's a page that I got these flower pictures from. Tucked inside each flower is a small black structure that is attached to something called a pollinarium (plural pollinaria). The pollinarium is the jackpot of pollen. It is a large amount of pollen in one neat package.

This is so cool. The pollinating insect, while moving around the flower looking for nectar, hooks a foot around the pollinarium and, if conditions are right, pulls the entire structure out of the flower. Upon removal, the pollinarium starts to dry, and the arms holding the packets of pollen, called translator arms, reorient themselves such that, you guessed it, when the insect lands on another (hopefully) milkweed flower, the pollinarium is inserted into the proper place on the new flower.

The fluff on attached to the seeds is an effective dispersal mechanism that helps spread offspring away from their parent plants, presumably to reduce competition. It is as good or better than down as an insulator.

A nice gallery of eastern US species can be found here.

Blue jay pic from here. Pollinarium from here. Pink flower pic from here. Orange ones from here.