A new species of Psidium (Myrtaceae) from the Brazilian Northeast LESLIE R. LANDRUM 1 AND CAROLYN ELINORE BARNES PROENÇA 2 1 School of Life Sciences, Arizona State University, Tempe, AZ 85287-4501, USA; e-mail: les.landrum@asu.edu 2 Depto. de Botânica, Instituto de Ciências Biológicas, Universidade de Brasília, Distrito Federal, Brazil; e- mail: cproenca@unb.br Abstract. Psidium sobralianum from northeastern Brazil is described and illustrated. It seems to be most similar to P. bahianum. Psidium sobralianum differs from P. bahianum in various ways: leaf ratio usually greater than 2 times as long as wide (versus generally less than 2 in P. bahianum); peduncles 1–5 mm long (versus 12–38 mm long in P. bahianum); mature flower buds 10–13 mm long, 7–9 mm wide, open, with petal globe exposed (versus ca. 8 mm long, ca. 5 mm wide, closed or minutely porate, with petal globe hidden in P. bahianum); locules with 4–5(–18) ovules (versus 28–33 in P. bahianum); and seeds 1–10, 5–7 mm long (versus 15–20, 3–4 mm long in P. bahianum). Psidium bahianum is exclusive to the humid forests of costal Bahia and P. sobralianum is found in the higher dry forests and Bcarrasco^ vegetation of Ceará and Maranhão and at lower elevations in Pará. Key Words: Brazil, Ceará, Chapada do Araripe, Maranhão, Myrteae, Pará, Psidium. Resumo. Psidium sobralianum do nordeste do Brasil é descrita e ilustrada. Parece ser mais semelhante a P. bahianum. Psidium sobralianum difere de P. bahianum de várias maneiras: a razão foliar é geralmente superior a 2 (versus geralmente inferior a 2 em P. bahianum); os pedúnculos têm 1–5 mm de comprimento (versus 12–38 mm de comprimento em P. bahianum); os botões florais maduros têm 10–13 mm de comprimento por 7–9 mm de largura, e são abertos, com a globo petalífero exposto (versus ca. 8 mm de comprimento por ca. 5 mm de largura, fechados ou diminutamente porados, com globo petalífero escondido em P. bahianum); lóculos com 4–5(–18) óvulos (versus 28–33 em P. bahianum); e sementes 1– 10, 5–7 mm de comprimento (versus 15–20, 3–4 mm de comprimento em P. bahianum). Psidium bahianum é exclusiva das florestas úmidas costeiras da Bahia, e P. sobralianum é encontrada nas florestas secas mais elevadas e carrascos de Ceará e Maranhão e em altitudes mais baixas no Pará. Psidium L. is one of about 50 genera in the richest tribe in Myrtaceae, Myrteae (Lucas et al., 2007), comprising 60–100 species (McVaugh, 1968; Govaerts et al., 2008). It ranges from Mexico and the Caribbean to Argentina and Uruguay, with populations in two Archipelagos in the Pacific, the Galapagos and Revillagigedo Islands. The genus can be distinguished by the pentamerous flowers with multiovulate locules; placenta often peltate; seed coat rough or dull, not lustrous, covered with a pulpy layer when wet; and the hard portion of seed coat (5–)8–30 cells thick at the narrowest point, with the cells thick-walled, elongate, and overlapping (Fig. 1H) (Landrum & Sharp, 1989; Landrum, 2003). In the past few years, molecular studies of Myrtaceae indicated that Psidium is a monophyletic group related to Acca O. Berg, Amomyrtus (Burret) D. Legrand & Kausel, Campomanesia Ruiz & Pav., Legrandia Kausel, and Pimenta Lindl. (Lucas et al., 2007; Murillo et al., 2013). These genera are members of the morphologically based sub- tribe Myrtinae (i.e., embryos with relatively small cotyledons and a large hypocotyl), which appears to be a paraphyletic group in the tribe (Lucas et al., 2007). In our studies of Psidium, we independently discovered this new species and have decided to describe it together and name it after our esteemed colleague, the insightful and diligent student of Brittonia 67(4): 324–327 (2015), DOI 10.1007/s12228-015-9396-y ISSN: 0007-196X (print) ISSN: 1938-436X (electronic) © 2015, by The New York Botanical Garden Press, Bronx, NY 10458-5126 U.S.A. Published Online: 20 October 2015