It isn't unheard of to see a few forest species flowering in mid-March. For example, Skunk Cabbage (Symplocarpus foetidus, above) is usually the first native species to flower in the pre-spring, often sending up its flowering spathe and spadix structure in wet mucky forested areas while there is still snow on the ground, sometimes even as early as mid-February. Although Skunk Cabbage was still flowering, some plants had already put up their leaves, a sign that the flowering structures will soon shrivel, leaving a dark brown fist-sized fruiting structure into the summer.
As its common name suggests, Harbinger-of-Spring (Erigenia bulbosa, above) is often one of the first native wildflowers to begin blooming in mesic forests, but mid- to late-March is usually the earliest that you begin to see the tiny carrot-family flowers of these plants peppering the forest floor.
Another early bloomer, Spring Beauty (Claytonia virginica, above) often starts flowering at about the same time as the preceding species. This is one of our commonest forest wildflowers. In addition, it can withstand more disturbance than many of its forest associates, and it sometimes can be found in mowed lawns that once supported trees and a rich understory but that sadly have been reduced to a near monoculture of non-native grass.
Limestone Bittercress (Cardamine douglassii, above) is another of the ephemerals that begins flowering in mid- to late-March during normal years. This mustard is very similar to and often confused with Bulbous Bittercress (Cardamine bulbosa), which often grows in areas that are more damp. The flowers of Limestone Bittercress are often tinged with lavender, but they can be white like those of Bulbous Bittercress. One way to tell the two species apart is to look at the upper stems and determine if they are hairy or not... Limestone Bittercress has pubescent upper stems, whereas the upper stems of Bulbous Bittercress are hairless.
One of our most overlooked and underappreciated early-blooming plants is the native shrub American Hazelnut (Corylus americana, above), which can often be found flowering in early March. As seen above, this shrub has female and male flowers in separate inflorescenses on the same plant. In the foreground, you can see the fuschia-colored stigmas of female flowers, while the male flowers in drooping catkins can be seen in the background.
A shrub that is much more conspicuous when in flower in spring in mesic to damp forests is Spicebush (Lindera benzoin), shown above. The yellow clusters of tiny flowers on this species are usually not evident in northern Indiana until early April. Later in the season, these flowers are replaced by bright red berries.
Yet another species that can usually be found flowering in moist woods beginning in mid-March is Sharplobe Hepatica (Hepatica nobilis var. acuta), pictured above. The leaves of this species are dark purple and persistent through the winter.
Mid-march in mesic forests also brings forth the blossoms of Cut-leaved Toothwort (Cardamine concatenata, above). Typical of mustards, the flowers of this species have four petals in a cross-like arrangement. Like many of the other spring wildflowers featured in this post, the flowers of this species arrive early to take advantage of the sunlight that can reach the forest floor prior to the overstory trees producing leaves.
Two species similar in appearance that are often mistaken for one another are shown above and below. Above is Rue Anemone (Thalictrum thalictroides), a solitary plant of slightly drier woods and slopes that usually begins flowering towards the end of March. Below is False Rue Anemone (Enemion biternatum), a colony-forming wildflower that usually begins flowering in moist woods in late March.
The stunning Bloodroot (Sanguinaria canadensis, below) usually starts flowering in late March at the earliest, but we saw several nice colonies of this plant on 18 March this year. Like many other spring wildflowers, the seeds of Bloodroot bear sugary, fleshy appendages known as elaiasomes; as a result, the seeds are dispersed by ants that are attracted to the elaiasomes.
Lindsay and I were pretty shocked to find some Dutchman's Breeches (Dicentra cucullaria, below) in bloom, since it normally doesn't begin flowering until the very end of March. Lindsay really liked the photo below, as it shows a tiny ant on the uppermost flower. Dutchman's Breeches is similar to another moist forest species, Squirrel Corn (Dicentra canadensis), which begins flowering just a tad later.
One of the most striking spring wildflowers has to be Marsh Marigold (Caltha palustris), shown below. The bright yellow blossoms of this buttercup family species can start to show as early as mid-March in normal years. You can find this one in wetter, mucky areas and along streams, nearly always associating with Skunk Cabbage.
Common Periwinkle (Vinca minor), pictured above, is often regarded as a highly aggressive species. I won't go so far as to say that it isn't, but I don't know that I've ever seen this species away from a home site, or away from a planted colony for that matter. It certainly spreads by rhizomes from its originally planted location, and I wouldn't recommend planting it, but I personally don't put it in the same class as invasives like Garlic Mustard (Alliaria petiolata) or Multiflora Rose (Rosa multiflora).
Behold, the harbinger of spring - Erigenia bulbosa! This photo was taken on March 19, 2005 at Fall Creek Gorge in Attica, Indiana. 
The ubiquitous spring beauty, Claytonia virginica. In the depths of winter, even the most common of plants can bring us joy. This photos was taken on April 1, 2006 at Mammoth Cave in Kentucky. 
When there isn't much florally happening on the forest floor in early spring, Hepatica acutiloba is at its best. This photo of sharp-lobed hepatica was taken at Dowagiac Woods in southwest Michigan on April 15, 2006. 
Upside-down, they do look like a Dutchman's breeches, don't they? I took this photo of Dicentra cucullaria at Bendix Woods in South Bend, Indiana on April 10, 2005. 
If you've seen the roots of Dicentra canadensis, you understand why it's commonly referred to as squirrel corn. This photo was taken on April 17, 2005 at Bendix Woods.
In mid-April, marsh marigold lights up forested wetlands and seeps. This photo of Caltha palustris was taken in LaPorte County, Indiana on April 19, 2006.
