Louteridium section Parcostamium T.F. Daniel & E. Tripp, 2018

Daniel, Thomas F. & Tripp, Erin A., 2018, Louteridium (Acanthaceae: Acanthoideae: Ruellieae: Trichantherinae): Taxonomy, Phylogeny, Reproductive Biology, and Conservation, Proceedings of the California Academy of Sciences 65 (2), pp. 41-106 : 68-69

2. Louteridium section Parcostamium T.F. Daniel & E. Tripp , sect. nov. TYPE.— Louteridium costaricense Radlk. & Donn. Sm.

Evergreen perennial herbs, shrubs, or small trees (to 3 m tall); herbaceous stems glabrous; leaves not seasonally/simultaneously deciduous, subsucculent, ± evenly distributed along stems; calyx 23–65 mm long (during anthesis); stamens 2.

The three species of this section ( L. costaricense , L. parayi , and L. tamaulipense ) together span the entire geographic range of the genus, and contain both the northern- and southern-most occurring species. These species do not appear to share morphological characteristics that are not otherwise found among species in other sections. Section Parcostamium differs from section Tetrandrium by having two (vs. four) stamens, leaves that are ± evenly distributed along stems (vs. clustered near apex) and are not seasonally/simultaneously deciduous (vs. seasonally deciduous), and generally longer calyces (23 to 65 vs. 5 to 32 mm). It differs from section Louteridium by its generally smaller habit (perennial herbs, shrubs, or small trees to 3 m tall vs. shrubs to trees to 12 m tall); leaf texture (subsucculent vs. membranaceous); and generally shorter pedicels (up to 58 vs. up to 95 mm long). The sectional name is derived from the first three letters of all species included in the section.