Abstract
The tribe Stipeae with an estimated number of ca. 600 species is part of the grass subfamily Pooideae and has near worldwide distribution. Its species are often dominant constituents of steppe vegetation and other grasslands, especially in Eurasia, the Americas and Australia. The taxonomy of Old World Stipeae has been studied to date primarily on the basis of morphology and anatomy, while existing molecular phylogenetic investigations have mainly dealt with New World or Australian taxa. We studied 109 new ingroup taxa with a focus on Old World Stipeae (in addition with an extensive outgroup sampling) using chloroplast and nuclear ribosomal DNA sequences (3′
trn
K region, ITS1–5.8S gene–ITS2), and discuss taxonomic key characters. Five highly supported monophyletic lineages were identified, some of which were rather unexpected: (a) the narrowly defined
Stipa
core clade, which is primarily Eurasian but extends into Africa north of the Sahara Desert, (b) the majority of Old World
Piptatherum
, (c) a “Transcontinental Stipeae Clade” encompassing Eurasian, African, American and Australian lineages, (d) a Himalayan to E Asian clade and (e) the single species
Achnatherum splendens
. The large “Transcontinental Stipeae Clade” contained several lineages of Eurasian Stipeae different from the
Stipa
core (a), i.e., genera
Aristella
,
Celtica
,
Oloptum
gen. nov.,
Stipella
stat. et. gen. nov., species of
Achnatherum
, and the species-rich lineages of
Nassella
/
Jarava
in America and of
Austrostipa
in Australia. In our circumscription
Ptilagrostis
was nested in (d), a clade (which included some species of
Achnatherum
and poorly studied Himalayan species ascribed to either
Stipa
or
Orthoraphium
) and whose internal structure remained unclear.
Oloptum
, gen. nov., is described, and the following combinations are made:
Achnatherum pelliotii
, comb. nov.,
Aristella keniensis
, comb. nov.,
Oloptum miliaceum
, comb. nov.,
Stipella
, stat. et. gen. nov.,
S. capensis
, comb. nov.,
S. nitens
, comb. nov.,
S. parviflora
, comb. nov.,
S. staintonii
, comb. nov., and
S. tigrensis
, comb. nov.