Monographs Details: Thyella tamnifolia (L.) Raf.
Authority: Britton, Nathaniel L. Flora Borinqueña.
Description:Species Description - This slender, herbaceous vine, with densely hairy stems, is readily separated from all its West Indian relatives, by its very dense clusters of blue flowers, subtended by large, leaf-like bracts. In Porto Rico it is an abundant plant of sandy areas of the northern coastal plain, and occurs locally in sandy soil elsewhere, especially along streams. The natural range of the species is westward through Santo Domingo, Haiti, and Cuba, eastward through the Virgin Islands, in the Lesser Antilles from Guadeloupe to Trinidad; in continental tropical America from southern Mexico to Paraguay, and it grows also in tropical Africa, perhaps introduced there. No English name has come to our attention; translation of the recorded Spanish one would be Hairy Morning-glory.
Thyella (Greek, a harpy, without apparent significance) is a genus established by Rafinesque in 1836, the species here illustrated typical. About 12 American species have been referred to it, only one of them existing in Porto Rico. The aggregated flowers, with leaf-like bracts distinguish them from Jacquemontias , which have much the same flower-structure. The 5, narrow, persistent sepals are alike; the bell-shaped corolla is plaited, 5-angled, or somewhat 5-lobed; the 5 stamens are shorter than the corolla; the ovary is 2-celled, the 2 styles united, the 2 broad stigmas flattened. The fruit is a small, 4-valved capsule.
Thyella tamnifolia (yam-leaved, from fancied resemblance), is slender, nearly prostrate, or twining, and 1.5 meters long, or shorter, or sometimes nearly upright and then 15 to 30 centimeters high. The broad, thin leaves are pointed, from 3 to 10 centimeters long, the base heart-shaped, the lower ones long-stalked, the upper short-stalked, both surfaces loosely hairy, or nearly smooth. The densely hairy stalks of the compact flower-clusters are from 2 to 15 centimeters long; the outer bracts of the clusters are about 3 centimeters long or shorter; the narrow, hairy sepals are about 15 millimeters long; the blue corolla is about 10 millimeters broad. The capsule is much shorter than the sepals, only about 5 millimeters in diameter, the few, brown seeds about 2 millimeters long.
Ipomoea tamnifolia Linnaeus, Species Plantarum 162. 1753.
Thyella tamnifolia Rafinesque, Flora Telluriana 4; 84. 1836.
Jacquemontia tamnifolia Grisebach, Flora of the British West Indian Islands 474. 1861.