Appendix 1.
Voucher information for species of Asclepias and related genera used in this study.
| Species | Voucher specimen [Herbarium] | Collection locality | GPS coordinatesa |
| Asclepias cryptoceras S. Watson | Weitemier 12-23 [OSC] | Grant Co., Oregon, USA | 44.47970, −119.57758 |
| A. engelmanniana Woodson | Lynch 11224 [LSUS] | Barber Co., Kansas, USA | 37.3, −98.7 |
| A. eriocarpa Benth. | Lynch 10923 [LSUS] | Lassen Co., California, USA | 41.09, −121.30 |
| A. flava (Kuntze) Lillo non N. E. Br. | Zuloaga & Morrone 7069 [OKLA] | Dist. Jujuy, Argentina | −24, −63.35 |
| A. humistrata Walter | Fishbein 5596 [OKLA] | Polk Co., Florida, USA | 27.761, −81.465 |
| A. involucrata Englem. ex Torr. | Lynch 12050 [LSUS] | Apache Co., Arizona, USA | 36.7, −109.7 |
| A. masonii Woodson | Fishbein 3101 [OKLA] | Mpio. Comondu, Baja California Sur, Mexico | 24.63, −112.14 |
| A. nyctaginifolia A. Gray | Fishbein 2445 [ARIZ] | Pima Co., Arizona, USA | 31.80, −110.81 |
| A. scheryi Woodson | Fishbein 5137 [OKLA] | Mpio. Cuautitlán, Jalisco, Mexico | 19.561, −114.203 |
| A. tomentosa Elliott | Fishbein 5608 [MISSA] | Franklin Co., Florida, USA | 29.916, −84.369 |
| Calotropis procera (Aiton) W. T. Aiton | Fishbein 5427 [OKLA] | Cultivated | |
| Matelea cynanchoides (Engelm. & A. Gray) Woodson | Rein 106 [OKLA] | Angelina Co., Texas, USA | 31.07995, −94.27735 |
a
GPS coordinates reported to the accuracy recorded or based on coarse geo-referencing based on the collection locality.