Key to the 19 presently known Vietnamese species of Typhonium Updated from Van et al. (2017). 1. Leaves perfectly trifoliolate........................................................................................................................................... T. thatsonense - Not as above .......................................................................................................................................................................................2 2. Sterile interstice of spadix entirely covered with staminodes ..................................................................................... T. flagelliforme - Only base of sterile interstice of spadix covered with staminodes.....................................................................................................3 3. Spathe limb thin, lanceolate, elongate-triangular...............................................................................................................................4 - Spathe limb thick, ovate to ovate-triangular.....................................................................................................................................14 4. Leaves fully pedate with 5 or 7 leaflets..............................................................................................................................................5 - Leaves entire and/or 3-lobed ..............................................................................................................................................................8 5. Leaves with 7 leaflets, leaf lobes linear to or linear-lanceolate............................................................................................. T. lineare - Leaves with 5 leaflets, leaf lobes ovate, elliptic to elliptic-lanceolate ...............................................................................................6 6. Spadix much longer than spathe.................................................................................................................................... T. vermiforme - Spadix almost as long as spathe .........................................................................................................................................................7 7. Ovaries obovoid; stigmas light yellow to white; staminodes subulate, with acuminate apices ................................... T. dongnaiense - Ovaries elongate or lageniform; stigmas red; staminodes elongate-clavate, with dilated and flattened apices........... T. bachmaense 8. Spadix longer than spathe...................................................................................................................................................................9 - Spadix as long as or shorter than spathe...........................................................................................................................................12 9. Spathe limb corrugated.....................................................................................................................................................................10 - Not as above .....................................................................................................................................................................................11 10. Staminodes folded 180 o apically .............................................................................................................................. T. phuocbinhense - Staminodes straight up to parallel to axis...................................................................................................................... T. corrugatum 11. Male zone cylindrical, staminodes cylindrical to conical ........................................................................................ T. khonkaenensis - Male zone subglobose, staminodes clavate ..................................................................................................................... T. acetocella 12. Leaves entire....................................................................................................................................................................... T. laoticum - Leaves incompletely trifoliolate .......................................................................................................................................................13 13. Stigma funnel shaped and lobed............................................................................................................................. T. stigmatilobatum - Stigma disciform and unlobed............................................................................................................................................... T. huense 14. Spathe limb very strongly circinnately recoiled over the entire length......................................................................... T. circinnatum - Not as above .....................................................................................................................................................................................15 15. Staminodes 5 mm long..................................................................................................................................................................17 16. Spathe 14–30 cm long, thecae opening by small pores....................................................................................................... T. hayatae - Spathe 4.5–5.0 cm long, thecae opening by elongate slits .............................................................................. T. vietnamense sp. nov. 17. Staminodes subulate .............................................................................................................................................................. T. blumei - Staminodes filiform..........................................................................................................................................................................18 18. Staminodes curly ............................................................................................................................................................. T. trilobatum - Staminodes not curly .................................................................................................................................................... T. penicillatum

Published as part of Van, Hong Thien, Le, Van Son, Nguyen-Phi, Nga, Nguyen, Quoc Dat, Nguyen, Tran Quoc Trung, Nguyen, Hieu Cuong & Luu, Hong Truong, 2021, A new species and a new record of Typhonium (Araceae) from southern Vietnam, pp. 201-208 in Phytotaxa 527 (3) on pages 206-207, DOI: 10.11646/phytotaxa.527.3.4, http://zenodo.org/record/5751368