ARRIAGA, MIRTA O.* AND MARY E. BARKWORTH. 1) Lab.Anatomía Vegetal, Museo Argentino de Ciencias Naturales, Av.A.Gallardo 470, 1405, Buenos Aires, Argentina., 2) Intermountain Herbarium, Utah State University, Logan, Utah 84322-5305, U.S.A. - Leaf anatomy in Nassella and other South American Stipoid Grasses.
The Stipeae is a widely distributed tribe of
grasses of 400-500 species. Nassella is one of the largest
genera in the Stipeae, comprising 112 species, of which 104 are native
to South America. This study is part of a larger project being
undertaken by the Stipeae Working Group to explore the
diversity within the Stipeae with the ultimate goal of developing a
strongly supported taxonomic revision of the tribe. We compared the
cross-sectional leaf anatomy of 28 species of Nassella with
species from Aciachne, Jarava, Piptochaetium and
Stipa subg. Pappostipa. The species of Nassella were
chosen to reflect the ecological and geographic distribution of the
genus and include all 6 species native to North America.
Anatomically, the species of Nassella fall into two major
groups, those with valvate leaves and those with flat leaves. The
species with valvate leaves have a cross-sectional leaf anatomy
similar to that found in the 15 species Stipa subg. Pappostipa
examined and approach that of Aciachne. The leaf anatomy of the
species with flat leaves was more similar to that of species of
Jarava [= Stipa subg. Jarava]. The anatomy of Nassella
lepida is intermediate between that of the two groups. The
cross-section of Nassella planaltima is similar in some
respects to that of Piptochaetium but differs in having upper
and lower girders associated with its vascular bundles and in having
no sclerenchyma in its phloem.
Key words: ecology., leaf anatomy, Nassella, South America, Stipoid