Polianthes howardii Verh.-Will. Polianthes howardii Verh.-Will. in Phytologia 34: 365-368. f. 1. 1976 sec. Espejo-Serna & López-Ferrari 2008=Agave howardii (Verh.-Will.) Thiede & Eggli in Kakteen And. Sukk. 50: 112. 1999 syn. sec. The Plant List 2013