AbstractMolecular phylogenetic analyses and morphological characters of the grass supersubtribe Poodinae (tribe Poeae, PPAM clade) were evaluated with the goal of determining the relationships of single‐flowered spikelet genera recently classified in subtribe Cinninae and the sister genus of the New Zealand endemic genusSimplicia. A total of 136 samples representing 40 genera and 105 species were analyzed for three plastid (matK,trnC‐rpoB,trnT‐trnL‐trnF) and two nuclear ribosomal DNA markers (ITS, ETS). The Cinninae subtribe, includingAniselytron,Cinna,Cinnastrum,Cyathopus, andSimplicia, was recovered as monophyletic with weak support only in the combined analysis with known/putative hybrid taxa removed.Cinna(excludingCinnastrum) resolved as paraphyletic due to the position of the morphologically distinctiveCyathopus. Cinninae are characterized by flat leaf blades, open panicles, small, strongly compressed, single‐flowered spikelets, with a rachilla extension, and lemmas that are awnless or with a short subterminal awn. The genusCinnastrumis resurrected forCinna poiformisand differs fromCinnain its broader glumes and subterete caryopsis with solid endosperm. Simpliciais likely most closely related to the southern and eastern Asian genusAniselytron, with which it shares unequal and short lower glumes and spikelet disarticulation above the glumes, in contrast to the other three genera of the subtribe. The HSAQN clade, which has mainly multi‐flowered spikelets and is sister to Cinninae, is named subtribe Hookerochloinae, includingArctagrostis,Hookerochloa,Nicoraepoa,Saxipoa, andSylvipoa. The DAD clade, which is known to be of reticulate origin postulated here as involving Cinninae, is named subtribe Dupontiinae, and includesArctohyalopoa,Arctophila,Dupontia, andDupontiopsis. These three subtribes, together with subtribes Alopecurinae, Beckmanniinae, and Ventenatinae (along with Brizochloinae not tested here), make up the well‐supported Alopecurinae superclade within supersubtribe Poodinae.