I upvoted @ZeissIkon's answer and you should, too.
There are many plants that grow in the shade here on Earth. A quick visit to your local garden supply business will get you a wealth of information as will a quick Google search for "list of shade loving plants". But I'd like to build on Zeiss' answer.
No serious effort to colonize Mars (or any other planet) would be expected to just uproot existing plants (OK, take seeds...) and haul them along. That's bad planning. Every gardener and farmer on Earth wold be shaking their heads in contempt and disdain.
Major undertakings are planned for.
And when it comes to plant life, you can believe somebody would (OK, should...) be taking the time to seriously wonder, "what do I need to do to Winter Wheat to make it a viable food crop on Mars?"
Therefore, I'm going to suggest a bit of a spin on your question: "What should be done to plants intended for Mars to maximize viability?"
Disclaimer: I am not a botanist. I like electrons, they like chlorophyll. Things in their world die, things in my world release a bit of smoke before causing heartburn. These are observations from someone who's lived the last 38 years with a horticulturist. Fair warning. Who knows the value of what I've absorbed. If you know of a better solution, please let me know in comments to get your name in lights and corrections made.
Note: @JohnMcD pointed out that the atmosphere on Mars is only about 1% of Earth's, meaning wind isn't a problem. But dust is. That's going to change my answer a bit.
Desirable Terrestrial plants will be those that...
- Convert CO2->O2 quickly.
- Release atmospheric O2 from ground nutrients.
- Release lower CO2 through respiration.
- Act as quick-growing ground cover.
- Are drought tolerant.
- Provide food & materials for settlers.
And through either genetic manipulation or good hybridization, goals for Mars plantations can be plants that...
- Grow deep roots to bind the soil.
- Grow broad, tough leaves to capture more sunlight and deal with the abrasive nature of dust.
- Grow taller with fewer low branches or leaves so collected dust falls off without the pile having a significant consequence.
- Have a wide leaf spread.
- Have superior nitrogen fixation.
- Have superior water retention.
And if we don't have these plants in stock, we need to create them. And you should believe that we would.
Asking for candidates is a list too long.
There are thousands of plants that are good candidates for all of that. Some would be more work than others to develop into good Martian species and varieties. Some will meet a specific need: like food crops (human and stock animals). Others for textiles (clothing) and still others for pharmaceuticals (medicine) and construction (e.g. wood). But your question about the nature of the plants is a good one!
But don't forget that most basic of rules: location, location, location.
After all the modifications we might make to plants for Mars, in the end, we need to care greatly about where we plant them. This means you'll be planting in the lee of hills to avoid collected dust. It also means that one type of plant life will break most of the "rules" I just gave you...
Off the top of my head, I can't imagine a more important plant than windbreak foliage on Mars. I call it "windbreak" because that's what we have on Earth. It would be better to call it "dustbreak." Ideally, this is a densely bushy tree standing as tall as you can get it with deep roots. The tree doesn't need a lot of leaves, but it does need to protect crops from the dust.
A Word about the Dust
To give you an idea of the problem, a Martian dust devil can reach 5 miles or 8 kilometers into the air. There isn't a tree that can stop that... but that isn't quite the point. No windbreak tree on Earth can stop all the wind, which can easily reach miles into the air as well. The goal of the break is to break up the effects of the storm, basically getting them to hop over the protected area.