Neotropical woody bamboos range from northern Mexico to southern Argentina and Chile. The most interesting aspect of bamboo biology is their flowering habit. The species that are the most intriguing are those that manifest a cyclic pattern of gregarious flowering after long vegetative periods. The flowering cycle has been described in very few species. The goal was to identify mass flowering events of woody bamboo species native to Argentina and neighboring areas, and to estimate the flowering cycle of each species. Sixteen species were surveyed: Chusquea culeou, C. deficiens, C. lorentziana, C. montana, C. quila, C. ramosissima, C. tenella, C. valdiviensis; Colanthelia rhizantha; Guadua chacoensis, G. paraguayana, G. trinii; Merostachys clausenii, M. multiramea, Rhipidocladum neumannii and R. racemiflorum. To reconstruct flowering dates, information from literature and herbarium collections was consulted and more than 990 records were gathered. Flowering cycles were estimated by recording the intervals between reported flowering events. Evidence of regular flowering cycles of ca. 30 years was found for most of the species considered. There is a remarkable concentration of flowering cycles about multiples of 15-16 years. Flowering synchrony among different species of woody bamboos was recorded for the first time in South America.

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Chusquea (Poaceae, Bambusoideae, Bambuseae) is the most diverse genus of woody bamboos in the world. In Andean Patagonian forests of southern Argentina and Chile, several species of Chusquea are the dominant components of the understory. Chusquea argentina and C. culeou fo. longiramea were described from that area on the basis of morphological characters. Some authors have considered C. argentina to be a valid species and others have treated this and C. culeou fo. longiramea as synonyms of C. culeou. This study contributes to the delimitation of these taxa. Based on morphology and anatomy, we clarify differential characters between C. culeou and C. argentina and restore the latter as a valid species. Chusquea culeou fo. longiramea is synonymized under C. argentina. According to data of mass flowering events recorded in southern Argentina and Chile, C. culeou and C. argentina become reproductive at different times. Anatomical descriptions of culm and foliage leaf blade epidermis and cross sections are provided for each species. Comparative tables based on diagnostic characters are also included.

Chusquea Kunth (Poaceae, Bambusoideae, Bambuseae) is the largest bamboo genus in the world. Approximately 13 species of Chusquea occur in the southern Andes of Argentina and Chile and all of them are endemic. In the present work, two new species found in high-altitude grasslands of the Andes mountain range in northwestern Argentina, Chusquea egluma and Chusquea floribunda, are described and illustrated. Morphological and anatomical characters are described and two identification keys for the Andean Chusquea species from northwestern Argentina are provided, one based on morphological characters (vegetative and reproductive), and the other on anatomical characters (culm and leaf epidermis and cross section). The new taxa and related species are compared in tables based on characters of taxonomic value.Resumen-Chusquea Kunth (Poaceae, Bambusoideae, Bambuseae) es el ge ´nero de bambu ´es ma ´s grande del mundo. Aproximadamente, 13 especies de Chusquea habitan en los Andes australes de Argentina y Chile, y todos ellos son ende ´micos. En el presente trabajo, se describen e ilustran dos nuevas especies de bambu ´es len ˜osos que habitan en pastizales de altura en los Andes del noroeste de la Argentina, Chusquea egluma y Chusquea floribunda. Se describen caracteres morfolo ´gicos y anato ´micos, y se presentan dos claves de identificacio ´n de las especies andinas de Chusquea del noroeste de la Argentina, una basada en caracteres morfolo ´gicos (vegetativos y reproductivos) y otra, en caracteres anato ´micos (epidermis y seccio ´n transversal caulinar y foliar). Se presentan tablas comparativas de caracteres de valor taxono ´mico de los nuevos taxones y especies relacionadas.