Type:— PARAGUAY: Boquerón: Filadelfia, 07/10/1979, fl, Schinini A. & Bordas E. 18165 (holotype: CTES! isotypes: C!, CORD!, MBM!, MO!).

Diagnosis:— Serjania perulacea var. chacoensis is a glabrous or whitish puberulous vine that differs from the other two varieties by the color of the pubescence and the inciso-dentate margin of the leaflet with obtuse glandular teeth.

Woody vine, glabrous or whitish puberulous, trichomes single and short, mainly in the abaxial face of the leaflets. Leaves imparipinate, 3-jugate, the lower jugae 3-5-foliolate or 2-jugate, 3-5-foliolate, leaflets subchartaceous; terminal leaflet ovate, wide ovate or obovate; 1.8–4.7 × 0.4–3.9 cm; apex retuse; base decurrent in terminal leaflet or acute in the others; margin inciso-dentate with 5–7 conspicuous obtuse glandular teeth.

Distribution:— Serjania perulacea var. chacoensis is distributed in Chaco and Formosa provinces, in Argentina; in Santa Cruz department, in Bolivia; and Boquerón and Presidente Hayes departments in Paraguay. This variety occurs mainly in dry Chaco.

Phenology:— Flowering between August and November, and fruiting between October and November.

Etymology:— The name of this variety refers to the habitat it occupies.

Representative specimens examined:— ARGENTINA: Chaco: Dep. General Güemes, 2 km al E de la Invernada por el camino que bordea al río Teuco, 19°S, 61°46´W, 04/March 2000, sterile, R. Fortunato et al. 6578 (BAB, CTES). Formosa: Dep. Patiño: 4 km del Puesto de Gendarmería San Ramón, por ruta a Misión Tacoagle, direcc. S., 16/November 1991, fl, R. Fortunato et al. 2378 (BAB, CTES); Fortín Sargento 1° Leyes, Ea. Pozo del Ciervo, Río Pilcomayo, 05/August 1981, fl, J. J. Valla et al. 120 (BAA, CTES). BOLIVIA: Santa Cruz: Prov. Cordillera: Boyuibe, 55 km hacia la frontera paraguaya vía F. Villazón, 04/October 1983, fr, S. Beck & M. Liberman 9420 (CTES, LPB); Aguarati Izozog, 19,15536°S, 62,28290°W, 13/ June 1998, sterile, G. Bourdy 2024 (CTES, USZ); Cuarirenda Izozog, 500 m al norte de la comunidad Cuarirenda, 15/September 1998, fl, G. Bourdy 2032 (CTES, USZ); Cuarirenda, 19°05´S, 62°29´W, 10/October 1992, fr, M. Villegas & R. Manchego 221 (CTES, USZ). PARAGUAY: Boquerón: Colonia Fernheim, Colonia 22 (Neuwiese), 08/November 1987, fr, P. Arenas 3306 (BACP, CTES); ibidem, 09/September 2003, fl, L. August 75 (CTES); ibidem, 01/October 1999, sterile, L. August 363 (CTES); ibidem, 06/October 1998, fl, J. Friesen 27 (CTES); ibidem, 25 km de Filadelfia, camino a Fortín Tte. Montanía, 22/August 1981, fl, A. Schinini et al. 21081 (CTES); ibidem, 15/June 1986, sterile, N. Soria 1244 (CTES, FCQ); Neuland, Parque Valle Natural, 22°34´S, 60°06´W, 18/January 1993, sterile, L. Pérez et al. 2741 (CTES, PY). Presidente Hayes: Colonia Meno, Misión Nueva Vida, 02/February 1976, sterile, P. Arenas 1523 (CTES); ibidem, Loma Plata, 12/November 1990, fl, R. Vanni et al. 1937 (CTES).