This section is from the book "Nature's Garden", by Neltje Blanchan. Also available from Amazon: Nature's Garden; An Aid To Knowledge Of Our Wild Flowers And Their Insect Visitors.
Flowers - Dull violet or lilac and white, about i in. long, borne in a loose spike. Calyx 5-parted, the sharply pointed sepals overlapping; corolla, a gradually inflated tube widening where the mouth divides into a 2-lobed upper lip and a 3-lobed lower lip; the throat nearly closed by hairy palate at base of lower lip; sterile fifth stamen densely bearded for half its length; 4 anther-bearing stamens, the anthers divergent. Stem: 1 to 3 ft. high, erect, downy above. Leaves: Oblong to lance shape, upper ones seated on stem; lower ones narrowed into petioles.
Flowering Season - May - July.
Distribution - Ontario to Florida, Manitoba to Texas.
It is the densely bearded, yellow, fifth stamen (pente = f\ve, stemon = a stamen) which gives this flower its scientific name and its chief interest to the structural botanist. From the fact that a blossom has a lip in the centre of the lower half of its corolla, that an insect must use as its landing place, comes the necessity for the pistil to occupy a central position. Naturally, a fifth stamen would be only in its way, an encumbrance to be banished in time. In the figwort, for example, we have seen the fifth stamen reduced, from long sterility, to a mere scale on the roof of the corolla tube; in other lipped flowers, the useless organ has disappeared; but in the beard-tongue, it goes through a series of curious curves from the upper to the under side of the flower to get out of the way of the pistil. Yet it serves an admirable purpose in helping close the mouth of the flower, which the hairy lip alone could not adequately guard against pilferers. A long-tongued bee, thrusting in his head up to his eyes only, receives the pollen in his face. The blossom is male (staminate) in its first stage and female (pistillate) in its second.
While this is the beard-tongue commonly found in the Eastern United States, particularly southward, and one of the most beautiful of its clan, the western species have been selected by the gardeners for hybridizing into those more showy, but often less charming, flowers now quite extensively cultivated. Several varieties of these, having escaped from gardens in the East, are locally common wild.
The Large-flowered Beard-tongue (P. grandiflorus), one of the finest prairie species, whose lavender-blue, bell-shaped corolla is abruptly dilated above the calyx, measures nearly two inches long. Its sterile filament, curved over at the summit, is bearded there only.
Handsomest of all is the Cobea Beard-tongue, a native of the Southwest, with a broadly rounded, bell-shaped corolla, hairy without, like the leaves, but smooth within. The pale purple blossom, delicately suffused with yellow, and pencilled with red lines - pathfinders for the bees - has the base of its tube creamy white. Few flowers hang from each stout clammy spike.
The more densely crowded spikes of the large Smooth Beard-tongue (P. glaber), a smaller blue or purple flowered, narrower-leaved species, that shows an unusual preference for moist soil throughout its range, is, like the other beard-tongues mentioned, better known to the British gardener, perhaps, than to Americans, who have yet to learn the value of many of their wild flowers under cultivation.
The tall Foxglove Beard-tongue (P. digitalis), with large, showy white blossoms tinged with purple, the one most commonly grown in gardens here, escapes on the slightest encouragement to run wild again from Maine to Virginia, west to Illinois and Arkansas. Small bees crawl into the broad tube, and butterflies drain the nectar evidently secreted for long-tongued bees, but without certainly transferring pollen. To insure cross-fertilization, the flower first develops its anthers, whose saw-edges grating against the visitor's thorax, aid in sifting out the dry pollen; and later the style, which when immature clung to the top of the corolla, lowers its receptive stigma to oppose the bee's entrance. Professor Robertson has frequently detected the common wasp nipping holes with her sharp jaws in the base of the tube. With remarkable intelligence she invariably chose to insert her tongue at the precise spots where the nectar is stored on either side of the sterile filament.