Molecular phylogenetic data and seed coat anatomy resolve the generic position of some critical Chenopodioideae (Chenopodiaceae – Amaranthaceae) with reduced perianth segments
Authors: Sukhorukov Alexander P. , Nilova Maya V. , Krinitsina Anastasiya A. , Zaika Maxim A. , Erst Andrey S. , Shepherd Kelly A. 
Published: October 2018

The former Chenopodiumsubgen.Blitum and the genusMonolepis(Chenopodioideae) are characterised in part by a reduced (0–4) number of perianth segments. According to recent molecular phylogenetic studies, these groups belong to the reinstated generaBlitumincl.Monolepis(tribe Anserineae) andOxybasis(tribe Chenopodieae). However, key taxa such asC.antarcticum,C.exsuccum,C.litwinowii, C.foliosumsubsp.montanum andMonolepisspathulatawere not included and so their phylogenetic position within the Chenopodioideae remained equivocal. These species and additional samples ofBlitumasiaticumandB.nuttallianumwere incorporated into an expanded phylogenetic study based on nrDNA (ITS region) and cpDNA (trnL-trnFandatpB-rbcLintergenic spacers andrbcLgene). Our analyses confirm the placement ofC.exsuccum,C.litwinowiiand C.foliosumsubsp.montanum withinBlitum(currently recognised asBlitumpetiolare,B.litwinowiiand B.virgatumsubsp.montanum, respectively); additionally,C.antarcticum, currently known asOxybasisantarctica, is also placed withinBlitum(reinstated here asB.antarcticum). Congruent with previous studies, two of the three accepted species ofMonolepis– the type speciesM.trifida(=M.nuttalliana) as well asM.asiatica– are included inBlitum. The monotypic genusCarocarpidiumdescribed recently with the typeC.californicumis not accepted as it is placed withinBlitum(reinstated here asB.californicum). To date, few reliable morphological characters have been proposed that consistently distinguishBlitum(incl. twoMonolepisspecies) from morphologically similarOxybasis; however, two key differences are evident: (1) the presence of long-petiolate rosulate leaves inBlitumvs. their absence inOxybasisand (2) a seed coat structure with the outer wall of the testa cells lacking stalactites (‘non-stalactite seed coat’) but with an obvious protoplast inBlitumvs. seed coat with the outer walls of the testa cells having stalactites (‘stalactite seed coat’) and a reduced protoplast inOxybasis. Surprisingly, the newly sequenced North AmericanMonolepisspathulatanested within the tribe Dysphanieae (based on ITS andtrnL-trnF+rbcL+atpB-rbcLanalyses).The phylogenetic results, as well as presence of the stalactites in the outer cell walls of the testa and lack of the rosulate leaves, confirm the distinctive nature ofMonolepisspathulatafrom allBlitumand, therefore, the recent combinationBlitumspathulatumcannot be accepted. Indeed, the morphological and molecular distinctive nature of this species from all Dysphanieae supports its recognition as a new monotypic genus, named herein asNeomonolepis(type species:N.spathulata). The basionym nameMonolepisspathulatais also lectotypified on a specimen currently lodged at GH. Finally, whileMicromonolepispusillais confirmed as belonging to the tribe Chenopodieae, its position is not fully resolved. As this monotypic genus is morphologically divergent fromChenopodium, it is retained as distinct but it is acknowledged that further work is required to confirm its status.