Plants with (and without) borders

Dr. Karen Samis thinks a lot about borders. Specifically, the borders that define the geographical range of plants.

“Each plant has an area where it grows, and an area where it does not. But what stops the plant from going further into new territory?” she asks. “My cousin once joked it was a lack of public transportation.”

“And while that’s funny, it’s partially correct!” says Samis. “Part of what a plant needs in order to extend its range is seed distribution. But getting there is only half the battle. A seed must be able to grow, find a mate, and survive to make more seeds. We want to understand why a population of plants can live next door to some nice habitat, but never live there.”

Samis is an Assistant Professor of Biology at UPEI. She’s been awarded an NSERC Discovery Grant to explore how the genetics of a plant mixes with its environment to determine the edge of its geographic range.

“I’m studying Cakile edentula, better known as sea rocket,” says Samis. “It’s a common coastal plant native to eastern North America, and is found on beaches from Newfoundland to Florida. It also has these fabulous little fruits that are shaped like rockets and that travel easily by water, hence the name. The seeds should have no problem getting from beach to beach.”

Cakile edentula (Sea rocket): Photo: K. SamisCakile edentula (Sea rocket): Photo: K. Samis

Samis says coastal plants are particularly interesting because the width of the range may be just a few dozen meters across, but the length can be hundreds or thousands of kilometres long.

“The width is determined by a couple of clearly defined borders – the ocean on one side, and the end of the beach on the other,” says Samis. “Length can be defined by a number of variables. Climate is clearly important at long distances.”

Samis’ five-year research program will start with questions about the behaviour and characteristics of populations of sea rockets from different climate zones along the east coast.

“And those questions will range from ‘how early in the year does the plant flower?’ to ‘what is the pattern of genetic variation from population to population?’”

Sea rocket is a convenient plant to study, explains Samis, because it falls in a family of plants that scientists understand pretty well. It’s related to broccoli, cauliflower, kale, and a less tasty plant known as Arabidopsis thaliana.

Arabidopsis thaliana (thale cress): Photo: K. SamisArabidopsis thaliana (thale cress): Photo: K. Samis

“Arabidopsis thaliana is the first plant to have its genome sequenced,” says Samis. “We also know which genes are involved in seed germination, flowering, growth, and lots of other processes. Because sea rocket is a related species, we can carry some of that information over.”

Samis’ project will eventually examine the genetics of sea rockets from different parts of the range including its introduced range in western North America, to try and understand just what creates the border of the geographic range.

“We expect that because the plant doesn’t grow north of Newfoundland, that it simply can’t. But how much of that is due to climate or genetics?” asks Samis. “Plants are pretty good at defying our expectations. I expect to find answers we could have never predicted.”