Taxonomic and Photographic Guide to the Acanthaceae of Tamaulipas, Mexico Author Daniel, Thomas F. Department of Botany, California Academy of Sciences, 55 Music Concourse Drive, San Francisco, California 94118, U. S. A. tdaniel@calacademy.org Author García-Morales, Leccinum J. Herbario, Departamento de Posgrado e Investigación, Instituto Tecnológico de Ciudad Victoria, Blvd. Emilio Portes Gil 1301, Cd. Victoria, Tamaulipas, México; Author Mora-Olivo, Arturo Instituto de Ecología Aplicada, Universidad Autónoma de Tamaulipas, División del Golfo 356, Cd. Victoria 87019, Tamaulipas, México; text Proceedings of the California Academy of Sciences 2021 2021-09-30 67 6 185 228 journal article 10.5281/zenodo.11513051 0068-547X 11513051 Hygrophila corymbosa (Blume) Lindau PHENOLOGY .— Flowering: March–May, October–December; fruiting: May. DISTRIBUTION .— Native to southeastern Asia; naturalized in Mexico (Tamps). HABITAT .— Riparian vegetation (irrigation canals). ELEVATION .— 80 meters. NOTES .— This cultivated aquatic (aquarium trade) sometimes escapes and becomes naturalized in the New World ( Fig. 3A, B ). The two species of Hygrophila in Tamaulipas appear in different sections of the key above; they can be readily distinguished from one another by the following couplet: 1a. Young stems and leaves of emergent shoots, calyces, corollas, and capsules pubescent with glandular trichomes; flowers in expanded dichasia or in thyrses (bearing expanded dichasia in axils of subfoliose bracts) in leaf axils; corollas purplish with white ridges, 8–16. 5 mm long; stamens 4..... H. corymbosa 1b. Young stems, leaves, calyces, corollas, and capsules glabrous or pubescent with eglandular trichomes; flowers in terminal spikes; corollas pale lavender, 4.5– 5.5 mm long; stamens 2......... H. polysperma REPRESENTATIVE SPECIMENS .— Mpio. El Mante , irrigation water channels, 22°44ʹ54.25ʺN , 099°ʹ00ʹ26.89ʺW , A. Mora-Olivo 15620 ( UAT ); Mpio. El Mante , 22°43ʹ56.66ʺN , 098°58ʹ09.20ʺW , L. Alvarez 121 ( UAT ) .