Unio carbonarius Lea, 1838
Lea, 1836. Synopsis Fam. Naiades: 19. [nomen nudum]
Lea, 1838. Trans. Amer. Phil. Soc. 6 [O. 2]: 37, pl. 11, fig. 32.
Type(s): LECTOTYPE [AS HOLOTYPE] USNM_84080A (by Johnson & Baker, 1973: 150), River Medellin, Vera Cruz, Mexico.

Unio (sec. Elliptio) plexus — Simpson (1900), Simpson (1914)
Unio (Elliptio) pliciferus var. carbonarius — Martens (1900)
Psoronaias plexus — Frierson (1927)
Barynaias plexus — Haas (1969)
Sphenonaias plexus — Cummings et al. (2025)

Unio plexus Conrad, 1838
Conrad, 1838. Monogr. Fam. Unionidae 1(10): 89, pl. 49, figs. 1-2.
Conrad, 1853. Proc. Acad. Nat. Sci. 6: 255.
Type(s): LECTOTYPE ANSP_129923, Vera Cruz, Mexico.

Unio (sec. Elliptio) plexus — Simpson (1900), Simpson (1914)
Unio (Elliptio) pliciferus — Martens (1900)
Unio plexus — Pilsbry (1904), Contreras-Arquieta (2000)
Psoronaias plexus — Frierson (1927)
Elliptio (Barynaias) plexus — Haas (1929), Haas (1930)
Barynaias plexus — Haas (1969), Graf & Cummings (2007), Bogan (2010), Graf & Cummings (2021), Czaja et al. (2023)
Sphenonaias plexus — Cummings et al. (2025)

Unio pliciferus Lea, 1838
Lea, 1836. Synopsis Fam. Naiades: 13. [nomen nudum]
Lea, 1838. Trans. Amer. Phil. Soc. 6 [O. 2]: 61, pl. 17, fig. 53.
Type(s): SYNTYPE USNM_84080, Mexico.

Unio (sec. Elliptio) plexus — Simpson (1900), Simpson (1914)
Unio (Elliptio) pliciferus — Martens (1900)
Psoronaias plexus — Frierson (1927)
Barynaias plexus — Haas (1969)
Sphenonaias plexus — Cummings et al. (2025)

Unio pliciferus var. B minor Fischer & Crosse, 1894
Fischer & Crosse, 1894. Miss. Sci. Mexique, Rech. Zool. 2(16): 581, pl. 69, fig. 4.
(homonym of Unio margaritifer var. minor Rossmässler, 1835; intro'd as intra-sp. of Unio pliciferus Lea, 1838)
Type(s): HOLOTYPE (MONOTYPY) MNHN_IM-2000-1812, Rio Medellin, Mexique.

Unio (Elliptio) pliciferus var. minor — Martens (1900)
— Simpson (1900)
Unio (sec. Elliptio) plexus var. minor — Simpson (1914)
Barynaias plexus — Haas (1969)
Sphenonaias plexus — Cummings et al. (2025)