Buddleja thyrsoides is a lowland species endemic from southern Paraguay to the deltas of the Río de la Plata and Paraná River in Brazil, Argentina and Uruguay.<ref name=Norman>Norman, E. M. (2000). Buddlejaceae. Flora Neotropica 81. New York Botanical Garden, USA</ref> The species was first described and named by Lamarck in 1792.<ref name=Lam.>Lamarck, J-B. (1792). Tabl. encycl. 1: 291, 1792</ref>
Buddleja thyrsoides is a dioecious shrub 1 – 3. m tall, with tan bark, the young branches covered with white tomentum. The leaves are sessile or subsessile, linear or linear-lanceolate, the blade 7 – 15 cm long by 0.4 – 3 cm wide, subcoriaceous, glabrescent above, and white tomentose below. The fragrant white leafy inflorescences are 5 – 15 cm long by 2 – 3 cm wide, comprising 1 – 2 orders of branches, 0.5 – 2 cm long with cymose clusters of 5 – 15 flowers; the tubular corollas 3 – 4 mm long.<ref name=Norman/>
Norman identifies two subspecies distinguished by narrower seeds and denser tomentum resp.:<ref name=Norman/>
- Buddleja thyrsoides subsp. angusticarpa
- Buddleja thyrsoides subsp. thyrsoides (synonyms= Buddleja chloroleuca Kraenzl., Buddleja salicifolia Vahl.)
Neither the species nor its subspecies are known to be in cultivation.