Podostemum atrichum Chodat & Vischer ("Podostemon atrichus"), Bull. Soc. Bot. Geneve, ser. 2, 9: 195. 1917.-TYPE: PARAGUAY. Yague, Aug 1914, Chodat & Vischer 337 (lectotype, designated by Royen, 1954: G!). Plant Description: Roots 0.6--2.9 (1.4) mm wide. Stems monomorphic, arising 0.8-11 (5.5) mm apart along root, 0.4-600 (6.7) mm long, larger stems often twisted. Leaves petiolate, perpendicular to the stem axis, reflexed or upright, arising in a ca. 180° distichous manner, highly variable in form, with 1-3 central axes from which segments arise in an irregular or verticillate manner, to 2-8 (5) times dichotomously or subdichotomously divided, or with a combination of dichotomous and trichotomous divisions, 2.2--41 (15.1) mm long; leaf divisions arising in a 3-dimensional manner (more or less perpendicular to the plane of the previous division); ultimate divisions 0.05-7 (1.7) mm long, 0.05--0.5 (0.2) mm wide, awl-shaped, v-shaped or u-shaped in cross section, apices acute or rarely apiculate or blunt, with a faint central vein or central vein absent; petioles 0.5-2 (1.1) mm long, oval to flattened in cross section; leaf bases symmetrical, attached perpendicular to the stem axis; flexible or rigid, often persistent and darkened on older stems; stipules composed of a boat-shaped extension of the sheathing leaf base, persistent, hardened and darkened on older stems, 0.2-1.4 (0.7) mm long, with 2-7 (3) straight or incurved, flattened triangular teeth, teeth 0.05-3 (0.7) mm long, lateral teeth typically longer than medial teeth. Flowers 1-5 (1) per stem; spathella 1.5-5.5 (2.9) mm long, 0.9-2.2 (1.2) mm wide, smooth to minutely papillate, apex rounded or with a nipple, sometimes with a cap-like apical segment that becomes reflexed after spathella rupture; tepals 3, linear or awl-shaped, straight or curved, apex acute; lateral tepals 0.5-1.9 (1) mm long; andropodial tepal 0.5-1.8 (0.9) mm long; andropodium 0.3-1.6 (0.8) mm long prior to anthesis, during anthesis to 1.3-5.2 (3) mm; stamens 2; filaments 0.3-1.1 (0.5) mm long prior to anthesis, during anthesis to 0.3-2.6 (1.4) mm; anthers 0.6--1.7 (1.1) mm long, 0.5--0.9 (0.7) mm wide; pollen dyads 27-35 (28) µm long, 15-23 (18) µm wide; ovary 0.7-2.7 (1.5) mm long, 0.4-2.1 (1.2) mm wide; stigmas entire, 0.2-1.5 (0.6) mm long prior to anthesis, during anthesis to 0.4-2 (1.2) mm; pedicels 0.3-2.5 (0.8) mm long prior to anthesis, during anthesis to 1.2-6.1 (3.7) mm. Capsules 1.3-2.7 (1.9) mm long, 0.9-1.9 (1.3) mm wide; 6 ribbed (3 each valve), suture margins also rib-like; pedicels in fruit 1.6--7.8 (4.2) mm long; seeds 0-97 (31) per capsule, 0.2--0.4 (0.4) mm long, 0.1--0.3 (0.3) mm wide.
Distribution. Southcentral Paraguay, southeastern Argentina (Corrientes, Misiones), southern Brazil (southern Goias, southern Minas Gerais, Parana, Rio Grande do Sul, Santa Catarina, Sao Paulo); locally abundant, often as dense growth on horizontal and vertical rock surfaces; 60-1200 m. Podostemum distichum can occur alone or with P. irgangii, P. muelleri, P. rutifolium subsp. rutifolium, Tristicha trifaria, and at least one species of Apinagia.
Representative Specimen. Argentina. CORRIENTES: Saito Pirareta, Depto. Cordillera, Krapovickas et al. 45709 (CTES, F, G, GH, MICH, TEX, U).-MISIONES: Arroyo Yerba, 36 km al N del R. Soberbio, hacia Saltos de! Mocona, Depto. Guarani, Hunziker et al. 10818 1/2 (TEX); Yguazu, Osten & Rojas 8165, 8166 (L, S); arriba de la Garganta de! Diablo, Iguazu, Dpto. Iguazu, Tur 1868 (LP); cataratas de! Iguazu, Iguazu, Tur 1869 (LP); ar royo Cunapiru, Saito Encantado, Depto. Ldor. Gral. San Martin, Tur & Guaglianone 1953 (LP); Rio Iguazu, at base of Saito Bossetti, Iguazu, Tur et al. 2129, 2133 (LP, MEXU, WCSU); Rio Iguazu, Dos Hermanas, Iguazu, Tur et al. 2135 (LP, MEXU, WCSU); arroyo Piray Gugzu, upstream of bridge, Tur et al. 2143 (LP, MEXU, WCSU); arroyo Paraiso, on road to Mocona, 34 km from Soberbio, Tur et al. 2145 (LP, MEXU, WCSU); Rio lguazu, Saito Felix de Azara, Parque Nacional lguazu, Iguazu, Van et al. 3434 (CTES, F); Saito Dos Hermanas, cataratas del lguazu, lguazu, Zavaro 358 (LP). Brazil. GorAs: Rio Douradinha, Glaziou 21988 (BR, C, G, K, L, RB, S, US); Rio Trinidade and Rio Cassu, Glaziou 21993 (B, K, L, C); Rio Trinidade, Glaziou 21994 (BR, G); Rio Bonito, 11 km N of Caiaponia, Philbrick et al. 5598 (ICN, MEXU, WCSU).-MINAS GERAIS: Rio Bugres, Caldas, Mosen 738 (C, L, S); small river passing under road (MG-050), 1 km due W of large hydroelectric dam (Furnas Dam), border of Sao Joao Batista do Gloria, Capitolio, Philbrick et al. 5686 (BHCB, ICN, MEXU, WCSU); W side of Alpinopolis, Philbrick et al. 5690 (BHCB, ICN, MEXU, WCSU); Rio Capavari (Rio Pardo), 13 km S of Botelhos, Philbrick et al. 5695 (BHCB, ICN, MEXU, WCSU); Rio Verde, Pocinhos do Rio Verde, 5-7 km SW of Caldas, Philbrick et al. 5699 (BHCB, ICN, MEXU, WCSU); Ribeirao da Caquiero, Regnell 2053 (L).-PARANA: Rio Dos Patos, Prudentopolis, Hatschbach & Guimariies 19187 (US, UNA); Foz do Chupim, Dois Vizinhos, Hatschbach & Guimaraes 20526 (UNA); Rio Chopim, 15 km N of Clevelandia, Lindeman & Haas 1151 (U); Rio Igu u. Igu u-Fiille, Igua u. Mattick 1000 (B); Rio Pedra Blanca do Araraquara, about 2 km N of Pedra Blanca do Araraquara along BR 376, Philbrick & Novelo 5784 (MEXU, R, WCSU).-RIO GRANDE DO SUL: Arroyo Alegre, Neu-Wurthemberg, Bommueller 738 (GH, L); Cascada de Hermenogilda, Serra dos Taypes, Lindman A775 (L, S); Silveira Martins, Lindman A1295 (L, S); 15 km SW of Lavras do Sul, Lindeman 6735 (U); Fazenda do Posto, Lindeman & lrgang 8663 (U); Rio Francesco Alves, Vale de Sul, Llnha Bernardino, Philbrick et al. 5003-5007 (ICN, MEXU, WCSU); along BR-392, 20 km NW of Pelotas, Philbrick et al. 5019, 5020 (ICN, MEXU, WCSU); small river running under BR-386, ca. 29 km NW of Soledade, Philbrick et al. 5055 (ICN, MEXU, WCSU); Rio Butia, waterfall, ca. 25 km W of Soledade, Philbrick et al. 5058-5061, 5063, 5064, 5066-5074 (ICN, MEXU, WCSU); Rio Tijela, 35 km S of Soledade, Philbrick et al. 5078-5081 (ICN, MEXU, WCSU); Rio Fao, near Pouso Novo, Philbrick et al. 5086-5088 (ICN, MEXU, WCSU); Rio Santa Cruz (Rio Cai), Saito (Elastro), Philbrick et al. 5095-5098 (ICN, MEXU, WCSU); Rio Pinto, 8 km NE of Sao Francisco de Paula on road to Cambara do Sul, Philbrick et al. 5099-5102, 5104-5108 (ICN, MEXU, WCSU); Rio Camisa, 7 km S of Cambara do Sul, Philbrick et al. 5112-5117 (ICN, MEXU, WCSU); small stream, 11 km N of intersec tion with road to Cambara do Sul, Cambara Co., Philbrick et al. 5120-5130 (ICN, MEXU, WCSU); Rio Moraes, 16 km S of Born Jesus, Philbrick et al. 5131-5136 (ICN, MEXU, WCSU); road to Vacaria, 3 km from center of Born Jesus, Philbrick et al. 5149-5151 (ICN, MEXU, WCSU); small stream running through pasture, 15 km W of Born Jesus, Philbrick et al. 5152-5155 (ICN, MEXU, WCSU); Rio Pelotas, 41 km N of Vacaria, Philbrick et al. 5156 (ICN, MEXU, WCSU); Rio Forqueta, Cascata Garapia, Barra do Ouro, Philbrick et al. 5187, 5188 (ICN, MEXU, WCSU); arroyo Chuvisquiro, bottom oflarge waterfall, 4 km from Riozinho, Philbrick et al. 5192-5196, 5198, 5201, 5203 (ICN, MEXU, WCSU); arroyo do Conouto, Riozinho, Philbrick et al. 5205, 5206 (ICN, MEXU, WCSU); Rio Vila Lageado Grande, Vila Lageado Grande, Philbrick et al. 5268, 5269 (ICN, MEXU, WCSU); arroyo Teixeira Soares, Marcelino Ramos, Philbrick et al. 5317, 5318, 5320, 5322 (ICN, MEXU, WCSU); Erechim, Philbrick et al. 5327A (ICN, MEXU, WCSU); Rio Vietnan, Erechim, Philbrick et al. 5335-5341 (ICN, MEXU, WCSU); Rio Poco, Erechim, Philbrick et al. 5344-5346, 5347B, 5348 (ICN, MEXU, WCSU); Rio Suzana, Gaurama, Philbrick et al. 5359-5368 (ICN, MEXU, WCSU); Rio Lageado, Marcelino Ramos, Philbrick et al. 5370,5371,5372B, 5375 (ICN, MEXU, WCSU); Rio Teizeira Soares, Viadutos, Philbrick et al. 5384-5386 (ICN, MEXU, WCSU); Rio Camisa, Cambara do Sul, Philbrick et al. 5539, 5540, 5542-5555 (ICN, MEXU, WCSU); Rio Pinto, San Francisco do Paula, Philbrick et al. 5557 (ICN, MEXU, WCSU); arroyo Caracol, Parque do Caracol, Canela, Philbrick et al. 5558 (ICN, MEXU, WCSU); Born Jesus, Aparados de Serra, Fazenda Bernardo Velho, Rambo 34957 (L, S); Vila Seca, Caxias, Rambo 54828 (B, S); Serra dos Taypes, Schwacke 2675 (C, RB); ravine S of Rio Pelotas, Vacaria, Smith & Klein 8173 (L, US); Rio Cerquinha, 32 km N of Born Jesus, Born Jesus de Serra, Smith & Klein 15819 (R, US); Lajeado Grande, Sao Francisco de Paula, Wasum 3396 (US).--SANTA CATARINA: Rio Capinzal, Dusen 17870 (NY, L, S, U); 2 km E de Paine!, Lajes, Krapovickas & Schinini 38352 (GH, MO); without locality, [date unknown], F. Muller s.n. (C), Muller s.n. (C); Rio Irani, confluence of two rivers, 15 km E of Chapeco, Philbrick et al. 5409, 5410, 5414, 5416, 5417, 5425-5428 (ICN, MEXU, WCSU); Rio Chapecozinho, Cascata Manela, Xanxere, Philbrick et al. 5435-5439, 5442, 5443, 5447, 5448 (ICN, MEXU, WCSU); Rio Chapeco, locality called Prainha, 10-15 km E of Abelardo Luz, Philbrick et al. 5455 (ICN, MEXU, WCSU); Rio Chapeco, Quedad do Rio Chapeco, 5 km W of Abelardo Luz, Philbrick et al. 5465, 5467-5471 (ICN, MEXU, WCSU); Rio Jacutinga, ca. 10 km W of Aqua Dulce, Philbrick et al. 5477 (ICN, MEXU, WCSU); Rio Sao Joao, E of Campos Novos, Philbrick et al. 5481-5488 (ICN, MEXU, WCSU); Rio do Sul, Alto Matador, Reitz 6110 (L, US); Rio Peperi-guacu. 15 km S of Dionisio Cerquiera, Reitz & Pereira 9675 (L, R, US); Rio do Sul, Alto Matador, Reitz & Klein 8312 (US); Sao Joaquim, Reitz & Klein 8491 (L, US); Rio Castelhanos, Cacador, Reitz & Klein 11874 (US); Blurnenau, Schenck 328 (B, C, L); Rio Itayahy, near Blumenau, Schenck 580 (L); without locality, Schwacke 103 (US); Rio ltajahy, Blurnenau, Schwacke 6069 (C, RB); Rio Peperi-guacu. Sao Miguel, Smith & Klein 12791 (R, US); Rio Chapeco, Abelardo Luz, Smith & Klein 13892A, 13891 (US); Rio Irani, 23 km E of Ponte Serrada, Joacaba, Smith & Reitz 9886 (L, R, US); Rio Taimbezinha, 1 km E of Born Jardirn da Serra (Cambajuva), Sao Joaquirn, Smith & Reitz 10188 (L, R, US); Sao Joaquim, E of Bom Jardim, Smith & Reitz 14191 (R, US); 12 km SW of Sao Joaquim, Smith & Reitz 14333 (VS); Rio Tubarao, near Pedras Grandes, Ule 1875 (L); Rio Capivare, Serra Geral, Ule 1877 (L).-SAO PAULO: Inst. Florestal rnides campos do Jordao, Cachoeira Dentro, Anderson & Faria 53597 (UEC); Rio do Peixe, Cachoeira do Monjolinho, a 6 km de Socorro estrada para Munhoz, Bove et al. 1115 (R, in spirit); without locality, Gaudichaud 10 (L); without locality, Glaziou 15444B (C); without locality, Glaziou 19815 (K); Rio Riacicaba, [collector unknown] 19818 (C); Campos do Jordao, Parque Estadual de Campos do Jordao, no Mirante das Ca choeiras, Yans & Marcelli 19544 (UEC). Paraguay. ALTO PARANA: Rio Acaray, 2 km de su desernbacadura al Rio Parana, Caballero 2500 (CTES); Yguazli, Chodat 337, 338 (G).-CORDILLERA: Saito Pirareta, town of Piribebuy, 80 km NE of Asuncion, Philbrick & Novelo 5631 (MEXU, WCSU).-PARAGUARI: Saito Pirareta, Sparre & Vervoorst 331 (CAN, G, GH, MT, US).-State unknown: [locality unclear], Balansa 2364 (G) ; Yague, 1914, Chodat s.n. (G) Uruguay. [locality unclear], Berro 5157, 5160 (C) ; Rio Negro, [collector unknown] 3 (C); Saito Grande, [collector unknown] 3328 (C).
Discussion. Podostemum distichum is distinguished by two features: 1) stipule divided into 2-6 teeth; 2) leaf divisions arising more or less perpendicular to the plane of the previous division, i.e., in a 3-demensional manner. This latter feature can be subtle, especially when leaves are long and flexible.
Podostemum distichum is morphologically the most variable species in the genus. The divided leaves can be dichotomous, subdichotomous, irregularly divided, or verticillate. Such variation can be found among leaves on the same plant. Stipular teeth vary in number and form (straight or curved). The apex of the teeth can be acute or blunt (not illustrated). The stipule texture also varies from thin and membra nous to thickened and rigid, the latter especially on large plants.
Podostemum distichum can be confused with P. irgangii in populations where the former produces semi-verticillate or verticillate leaves (Philbrick & Novelo 2001). It is notable that a few leaves on the type material of P. distichum (Sellow in B, L) are verticillate. Warming (1889, Plate XIX, Fig. 5) illustrated a verticillate leaf in his account of P. distichum, although it is unclear whether this leaf represents a mixed collection with P. irgangii or a verticillate leaf of P. distichum. It is notable that none of the numerous iso types of P. distichum have the stipule types found in P. irgangii.
We have placed in synonymy under P. distichum the names of four species that Royen (1954) recognized (P. aguirense, P. atrichum, P. glaziovianum, P. schenckii). Royen (1954) distinguished these taxa largely on leaf and stipule form. We have found no reliable features with which to separate them as species distinct from P. distichum.
Podostemum distichum was first described as Lacis disticha by Charnisso in 1833; the only reference to a specimen is the note "Brasilia aequinoctialis. Sellow." Duplicates of this Sellow collection are in B, BR, G (3), K, L (4), LE (2) and W (5). Charnisso at the time worked in Berlin, and we consider the specimen in B as the holotype. Royen (1954, p. 232), perhaps unaware that the B sheet was still extant, listed the type (i.e., lectotype) as deposited in W (it is unclear to which of the five duplicates in that herbarium he refers).
In the protologue for Podostemum aguirense Chodat and Vischer (in Chodat 1917) cite only one collection " No. 338, Chodat et Vischer," from "Yguazu." One specimen in G (acc. no. 8308/1) corresponds to the specimen cited by them, although Vischer's name is not on the label. We consider this specimen the holotype.
Warming (1899, p. 130) listed B as the repository of the type of Podostemum glaziovianum Warm. One specimen in B corresponds to the information cited by Warming, which we consider the holotype. lsotypes are located in C and L. The "type" indicated by Royen (1954, p. 237) as located in C is an isotype. Royen also cited a duplicate in P, which was not examined by us.
A specimen corresponding to the information provided with the species description of Podostemum warmingii (Chodat 1917, p. 240) is located in G (no. 8308/60), although Vischer's name is not included on the label. We interpret this specimen as the holotype.