Key for Chelonanthus (Griseb.) Gilg

1Corolla blue to purple; anthers recurved after anthesis
1'Corolla green, white, cream, or yellow; anthers straight or slightly curved after anthesis
2Stem strongly quadrangular, 4-angled to 4-winged along entire length
2'Stem terete to weakly quadrangular, only 3-4 of most basal internodes may be strongly quadrangular and 4-winged
3Upward facing hook present near apex of glandular dorsal area of calyx; bracteole apex acuminate to cuspidate
3'Glandular dorsal area of calyx lacking an upward facing hook; bracteole apex acute to obtuse
4Calyx lobe circular; corolla tubular to salver-shaped; sexual structures positioned within corolla tube; mature fruit orientation erect to horizontal
4'Calyx lobe ovate; corolla funnel-shaped to campanulate; sexual structures positioned near corolla lobes or slightly exserted; fruit orientation nodding
5Plant up to 2.5 m high; stem quadrangular for 3-4 of most basal internodes then abruptly becoming terete, if wings present then 0.1-1.8 mm wide; stigma lobe elliptic; fruit orientation nodding
5'Plant up to 1.6 m high; stem terete to weakly quadrangular along entire length, if wings or ridges present then 0.1-0.3 mm wide; stigma lobe orbicular; mature fruit orientation horizontal to erect
6Leaves elliptic to ovate; calyx 6-14 x 5-10 mm, lobes fused for 1/6-1/5 of total length
6'Leaves linear, sometimes lanceolate to elliptic; calyx 4-9 x 3-7 mm, lobes fused for ca. 4/5 of total length