Flower:

Spike-like raceme up to 12 inches long at the top of the stem, with smaller auxiliary racemes arising from upper leaf axils. Flowers are blue-violet to purple, 3/8 to 1 inch (1 to 2.5 cm) long, tubular, the upper lip forming a rounded hood over the mouth of the tube. The lower lip is broad, 3-lobed, violet to white and speckled with darker purple.

The calyx holding the flower is green to purplish and about 1/8 inch (~3 mm) long. At the base of the short flower stalk is a small, leaf-like bract. The stalk, bract and calyx are all covered in spreading, glandular hairs.

Leaves and stems:

Leaves are 1 to 4 inches (to 10 cm) long, up to 3 inches wide, opposite, heart-shaped with a pointed tip, toothed with rounded or bluntly pointed teeth, veiny, hairless to sparsely hairy on the upper surface with soft short hairs on the underside, on a hairy stalk up to 2 inches long. Stems are erect, stout, square, branched in the upper plant and densely covered in glandular and/or non-glandular hairs. Plants may form colonies from horizontal stems (stolons and rhizomes).

Fruit:

The calyx swells into a capsule, containing brown nutlets.

Notes:

Heart-leaved Skullcap is a rare species in Minnesota, limited to the Mississippi River valley and its tributaries in our southeast counties, where it reaches the northern fringe of its range. According to the DNR, it was originally listed as a Special Concern species in 1984 and elevated to Threatened in 1996 after biological surveys conducted in the 1990s found only 7 populations. It is at risk primarily from destruction of its forest habitat due to agriculture, grazing, logging, road construction, disruption of the natural river water level cycles, and (of course) invasive species such as buckthorn and garlic mustard. It is currently listed Special Concern in Wisconsin.

While USDA currently lists 9(!) subspecies of S. ovata, these are not universally recognized and the distinguishing characteristics are not well documented, though some of the factors seem to be whether hairs are glandular, density of hairs, whether the floral bracts are longer than the calyx, whether bracts are stalked or toothed, and largest leaf size. The species found in Minnesota is subsp. ovata (also known as var. versicolor), which is glandular hairy, has floral bracts that are usually stalkless and toothless and consistently shorter than the calyx.

Nancy Braker at the Cowling Arboretum, where my photos were taken, says the leaves on the population there are consistently ravaged by an unknown insect and always look pretty ragged. A recent post on Facebook of plants seen along the Mississippi River showed the same ragged leaves. I am curious to know what critter has a fondness for this species...