Spring comes suddenly in the north. One day, there's nothing but dirty snow shrinking away from dry, dead grass. The next day, it seems, a flower pops up.

Usually, the first spring flower people notice in the southern Yukon is the prairie crocus, says Bruce Bennett of the Canadian Wildlife Service in Whitehorse. Its soft purple flowers appear on dry, sunny slopes in late April.

The prairie crocus, like the sunflower, is a heliotrope. That means its flower turns through the day to follow the sun, the botanist explains.

"The petals act like a satellite dish to focus the light and warmth of the sun into the flower," he says. Small insects like ants crawl into the centre of the flower, where the temperature is significantly warmer, and move around pollenating the flower.

The crocus is especially well adapted for spring flowering, says Bennett. The fine hairs on its leaves reduce water loss by protecting the leaves from the wind. The crocus blooms while the flower is still close to the ground and well-protected but, unlike most plants, the stalk continues to grow even after the flower has been pollinated so that the seed pod forms as high as possible for better seed distribution.

Although the prairie crocus is the first flower most people notice in the spring, it's not the first to appear, says Bennett. Willows and soapberries blossom even earlier, but their flowers are far less showy. The willow flower is the catkin, or pussywillow, the furry bud that appears on spring branches. The low, shrubby soapberry has tiny, inconspicuous, yellow-brown flowers that appear along the stem before the leaves open.

Most Yukon flowers are perennials, Bennett says, because annuals are too vulnerable to a bad year to survive long in the north. One of the few exceptions is the fairy candelabra, a small plant classed with the primrose family. Its leaves sprout in a clump near the base of a long, slender stalk. At the top of the stalk is a spray of tiny white flowers. The plant grows in sandy and gravely places, such as south-facing slopes along the Old Alaska Highway, Bennett says.

Several families of flowers follow the earliest blooming varieties. The roses have begun to blossom in the southern Yukon, and that includes more plants than one might expect.

"Botanists group all plants by their flowers, so some things that don't seem to be similar are related," explains Bennett. The rose family includes strawberries and the large group of plants called cinquefoils.

"The next big wave that we'll see is the peas," Bennett says. "That includes lupines, licorice-root, milk-vetches or locoweeds, alfalfa, sweet clover and clovers."

Some of the spring flowers are more retiring and less plentiful than the peas, but no less beautiful. The calypso orchid, or fairyslipper, is an example. Its large rose-purple flower droops from a delicate stem carrying a single leaf. The orchid grows in shaded spruce forests, like Wye Lake Park near Watson Lake. To flower, it needs the help of a fungus that lives in the leaf litter on the forest floor. It might be possible to transplant the plant, Bennett says, but once it is removed from the leaf litter and the fungus, it will rarely flower again.

As the days get longer and the earth warms up, more and more flowers appear. A lot of northern plants are red when they first come up through the ground, Bennett says. The red colour is an adaptation to reduce cell damage from ultraviolet light. It's common in alpine plants further south, but fairly widespread even at lower elevations in the Yukon, he says. As the plants grow and mature, the leaves and stems turn green and normal-coloured flowers open.

"The height of the bloom is the second week of July," says Bennett. After that, the appearance of new flowers tapers off and the plants put their energy into seed production. Occasionally, if a cool spell is followed by warm weather late in the summer, a few of the early plants will flower again.

"I've seen the prairie crocuses flowering again at the end of August out at Fort Selkirk," Bennett says.

For more information about Yukon plants, contact the Canadian Wildlife Service, Environment Canada, Whitehorse.