A New Species of Guadua (Poaceae: Bambusoideae: Bambuseae) Endemic to Nayarit, Mexico

Background: We found a flowering population of Guadua near the town of Heroico Batallón de San Blas, Nayarit. Unlike previously known populations of Guadua in the state, all of which appear to be G. paniculata, this population was morphologically similar to G. amplexifolia, a species known from southern Mexico, Central America, and northern South America but apparently absent from Nayarit. Question: Does the Nayarit population of Guadua represent a new species? Studied species: Guadua, Guadua lacerata. Study site and dates: Nayarit, Mexico, September 2023, April 2024. Methods: We did field observations and collected herbarium vouchers, measuring morphological vegetative and reproductive characters in the herbarium specimens and living plants. We used scanning electron microscopy to describe the foliage leaf, lemma, and palea micromorphology. Finally, we completed a conservation assessment. Results: This population of Guadua from Nayarit differed from G. amplexifolia in that it had relatively short culm leaf blades compared to the sheath, with the sheaths shredding from the base with age, highly floriferous pseudospikelets, and relatively short, densely pubescent lemmas. We describe the Guadua comprising this population as a new species named Guadua lacerata. We hypothesize that this species would be listed as Critically Endangered. Conclusions: Currently, Guadua lacerata is considered a new Critically Endangered species endemic to Nayarit, Mexico.