This section is from the book "An Illustrated Flora Of The Northern United States, Canada And The British Possessions Vol3", by Nathaniel Lord Britton, Addison Brown. Also available from Amazon: An Illustrated Flora of the Northern United States, Canada and the British Possessions. 3 Volume Set..
Annual or biennial glabrous slender branching herbs, with opposite, mostly dentate and sessile leaves, and small purplish peduncled flowers solitary in the axils. Peduncles not bracteolate. Calyx 5-parted, the segments linear. Corolla irregular, the tube somewhat expanded above, the limb 2-lipped; upper lip 2-cleft, erect; lower lip larger, 3-lobed, spreading. Fertile stamens 2, included, their anther-sacs divergent; sterile stamens 2, 2-lobed, one of the lobes capitate, glandular, the other glabrous, shorter. Style slender; stigma slightly 2-lobed. Capsule oblong or ovoid, septicidally dehiscent. Seeds numerous, wrinkled. [Greek, mud-flower.]
About 10 species, of wide geographic distribution. Besides the following, 2 or 3 others occur in the southeastern United States. Type species: Ilysanthes riparia Raf.
Peduncles longer than the leaves; calyx-segments shorter than the capsule.
1. I. dubia.
Peduncles shorter than the leaves; calyx-segments mostly as long as the capsule, or longer.
2. I. attenuata.
Stem slender, mostly erect, at length diffusely branched, 3'-8' long. Leaves ovate, ovate-oblong, or the lower obovate, sessile or very nearly so, or slightly clasping at the base, remotely denticulate or entire, obtuse or acutish at the apex, thickish, 3-7-nerved, 1/2'-1' long, the upper ones commonly much smaller; peduncles slender, considerably exceeding the leaves; flowers 3"-5" long; calyx-segments linear, about one-half the length of the corolla, shorter than the capsule; capsule narrowly ovoid-oblong, bluntish, 2"-3" high; seeds 1" long, reddish, the ends usually truncate.
In wet places, Massachusetts to Florida, west to Ontario, Minnesota and Texas. Also on the Pacific Coast, and in the West Indies and South America. July-Sept.
Lindernia attenuata Muhl. Cat. 59. 1813. Ilysanthes gratioloides curtipedicellata Bush, Bull.
Torr. Club 21: 494. 1894. I. attenuata Small, Bull. Torr. Club 23: 297. 1896.
Stem erect or ascending, 3'-16' long, the branches spreading. Leaves oblong to ovate, or sometimes obovate, 1/2' - 1 1/2' long, thinnish, obtuse, serrate with a few low teeth, 3-5-nerved, narrowed into short petioles, or sessile; peduncles shorter than the leaves; calyx-segments linear-subulate, as long as the capsule, or longer; corolla 2"-6" long; capsule narrowly ovoid, about 2" long, pointed; seeds slightly curved, 1 1/2"- 2" long, yellowish brown, the ends usually rounded.
In wet places, New Brunswick and Ontario to Wisconsin, south to Florida and Arkansas. Ascends to 2000 ft. in Virginia. Perhaps not specifically distinct from the preceding. May-Oct.