Podostemum comatum Hicken ("Podostemon comata"), Revista Chilena Hist. Nat. 21(6): 149. 1917.-TYPE: ARGENTINA. Misiones: lguazu, 6 Apr 1913, Rodriguez 791 p.p. (lectotype, here designated: SI! specimen on left side of sheet; isolecto types: BA, S! large central specimen on sheet). [The second element is P. distichum.]
Podostemum dimorphum P. Royen, Acta Bot. Neerl. 3: 258, pl. 2. 1954.-TYPE: BRAZIL. Parana: without locality, Dusen 16540 (lectotype, here designated: U!; isolecotypes: CM! L-2 sheets! NY! P! S-2 sheets! U-8 sheets!).
Podostemum undulatum P. Royen, Acta Bot. Neerl. 3: 259. 1954.-TYPE: BRAZIL. Santa Catarina: Rio Itayahy, near Blumenau, Apr, Ule 804 (holotype: P; isotypes: L-2 sheets!).
Podostemum undulatum var. angustifolium P. Royen, Acta Bot. Neerl. 3: 259. 1954.-TYPE: PARAGUAY. Alto Parana: Mbuvera, arroyo Iguazu, Jorgensen 4949 (holotype: C!; isotypes: DS! L! NY! S!). [The collection number was cited incorrectly in the protologue as "4989."]
Roots 0.8-2.6 (1.7) mm wide. Stems dimorphic, arising 1.1-17 (5.9) mm apart along root; vegetative stems 0.2-720 (12) mm long, larger vegetative stems often twisted; floriferous stems arising from root or as branches on vegetative stems, 0.5-11.5 (1.8) mm long. Leaves petiolate, upright or trailing, arising in a ca. 180° distichous manner, simple (basal leaves only) to 2-11 (5) times dichotomously or subdichotomously divided, 1.8-140 (44) mm long; leaf divisions arising in a 2-dimensional manner; ultimate leaf divisions 0.2-16.1 (4.4) mm long, 0.05-2 (0.4) mm wide, awl-shaped or linear in outline, flattened in cross section, apices acute, blunt or rounded, with a faint central vein or central vein absent; petioles 0.7-74 (9) mm long, round, elliptical or flattened in cross section; leaf bases symmetrical, attached perpendicular to stem; stipules composed of an extension of the boat-like sheathing leaf base, on young (short) stems typically caducous, on older (long) stems persistent or absent, when persistent hardened and darkened, 0.1-2.6 (0.6) mm long, entire or with 2-3 (2) straight or curved, flattened triangular teeth, teeth 0.05-1.7 (0.2) mm long. Flowers 1-4 (1) per stem, spathella 2.4-3.6 (3) mm long, 1.1-1.9 (1.5) mm wide, smooth to minutely papillate, apex rounded or with a nipple; tepals 3, lin ear or awl-shaped, straight or curved, apex acute; lateral tepals 0.5-2.1 (1.5) mm long; andropodial tepal 0.4-1.9 (1.9) mm long; andropodium 0.4-1 (0.7) mm long prior to anthesis, during anthesis to 1.3-3.4 (2.5) mm; stamens 2; filaments 0.4--0.8 (0.6) mm long prior to anthesis, during anthesis to 0.3-2.3 (1) mm; anthers 0.9-1.5 (1.3) mm long, 0.6--0.8 (0.8) mm wide; pollen dyads 27-35 (30) µm long, 17-25 (20) µm wide; ovary 1-2.7 (1.6) mm long, 0.7-1.5 (1.1) mm wide; stigmas entire, 0.4-1 (0.6) mm long prior to anthesis, during anthesis to 0.5-1.6 (1.2) mm; pedicels 0.4-1.1 (0.7) mm long prior to anthesis, during anthesis to 1.5-5.5 (4) mm. Capsules 1.5-2.6 (2) mm long, 1-2.4 (1.2) mm wide; 6 ribbed (3 per valve), suture margins also rib-like; pedicels in fruit 1.2-5.7 (4) mm long; seeds 0-68 (36) per capsule, 0.2--0.4 (0.3) mm long, 0.1--0.3 (0.2) mm wide.
Distribution. Southeastern Paraguay, northeastern Argentina (Corrientes, Misiones), Brazil (Rio Grande do Sul, Sao Paulo), and Uruguay; locally abundant, on vertical to near vertical surfaces of waterfalls, on near horizontal surfaces of rocks in the deepest and swiftest moving currents; 20-800 m.
Podostemum comatum can occur alone or with P. distichum, P. rutifolium subsp. rutifolium, P. muelleri, and Tristicha trifaria.
ADDITIONAL SPECIMENS EXAMINED. Argentina. CORRIENTES: arroyo Chimiray, Depto. Santo Tome, Cristobal & Krapovickas 1767 (CTES); arroyo Ciciaco, 6 km SW of Colonia Garabi, Depto. Santo Tome, Tressens et al. 2923 (CTES).- MISIONES: lguazu, Cabrera et al. 58 (LP); Rio Pepiri Guazu, Bernardo de Irigoyen, Depto. Gral M. Belgrano, Morrone et al. 2063 (MO); Salto San Martfn, Cataratas, Tur 1140 (LP); Rio Iguazu, Parque Nacional Iguazu, base of Saito Bossetti, Depto. Iguazu, Tur et al. 2128 (LP, MEXU, WCSU). Brazil. PARANA: Rio ltarare, Morungava, Dusen 16540 (CM, K, L, MICH, NY, P, S, L, U); Rio Alegre, Fda. Monte Alegre, Fda. Velha, Hatschbach 4583 (US).-RIO GRANDE DO SUL: arroyo da Porta, Santo Angelo, Colonia Santo Angelo, Lindman A1199 (L, S); arroyo that drains into Rio Camaque, ca. 5 km SE of town of Piratini, Philbrick et al. 5015, 5016 (ICN. MEXU, WCSU); along BR-392, ca. 1-2 km NW of town of Piratini, Philbrick et al. 5017 (ICN, MEXU, WCSU); arroyo do Lajeado, road from Pedro Osoria, ca. 20 km NE of town of Santo do Erval, Philbrick et al. 5022, 5027 (ICN, MEXU, WCSU); road to Santo do Erval, ca. 40 km S of Pinheiro Machado, Philbrick et al. 5028 (ICN, MEXU, WCSU); small river that passes under BR-293, ca. 45 km SE of Dom Pedrito, Philbrick et al. 5030 (ICN, MEXU, WCSU); Rio Taquarembo, 44 km N of Santiago on road to Bocaruca, town of Tupantuba, Philbrick et al. 5045-5048 (ICN, MEXU, WCSU); Rio Urucua, along route BR- 285, ca. 20 km E of Sao Lufs Gonzaga, Philbrick et al. 5049 (ICN, MEXU, WCSU); Rio Vila Lageado Grande River, town of Vila Lageado Grande, Philbrick et al. 5267 (ICN, MEXU, WCSU); Erechim, Philbrick et al. 5343 (ICN, MEXU, WCSU); Rio Poco, steep cliffed waterfall, town of Erechim, Philbrick et al. 5347A (ICN, MEXU, WCSU); Rio Castilhos, town of Getulio Vargas, Philbrick et al. 5352 (ICN, MEXU, WCSU); Cacapava do Sul, Pirani & Yano 520 (SP).-SAO PAULO: Rio do Carmo, Parque Estadual Interuples, Trecho do Alecrim, Iporanga, Melo s.n. (UEC).-SANTA CATARINA: arroyo Guaza, Blumenau, Jorgensen 4949 (US); Rio Itayahy, Blumenau, Ule 804 (L, US). Paraguay. AMAMBAY: Cerro Cora, Schinini & Bordas 20242 (C, G).--GUAIRA: Guayna Mannera, Pedro 4949 (C, DS, L, NY, S, US); Rio Tebicuary-mi, town of Mbocayaty, Philbrick & Novelo 5633, 5634 (MEXU, PY, WCSU). Uruguay. Rio Negro, Berro 3 (-294) (C); without locality, Berro 5158 (C).
Podostemum comatum is the only species in the genus that has dimorphic stems. The species can be difficult to identify, however. Although plants of P. comatum typically are larger than those of P. rutifolium, their sizes overlap for essentially all vegetative characters. Small vegetative plants of P. comatum are not readily distinguishable from those of P. rutifolium. Only when plants are in flower or fruit can P. comatum be confidently separated from P. rutifolium.
Our circumscription of P. comatum is broader than that of previous authors (e.g., Royen 1954; Tur 1997). Two other species (P. dimorphum, P. undulatum) have been described that also exhibit stem dimorphisms. We believe that P. dimorphum and P. undulatum represent environmental forms of P. comatum, which we regard as a fairly widespread species in southern Brazil and Argentina. The types of P. dimorphum and P. undulatum fall within the range of variation that we have observed in populations of P. comatum.
Some authors (e.g., Tur 1997) noted that stems of P. comatum are twisted and have used this character as diagnostic for the species. We have observed twisted stems occasionally in several species of Podostemum (e.g., P. distichum, P. rutifolium, P. ceratophyllum). In each case, twisting was observed on large plants when they grew on vertical surfaces in falling water. Why the twisting occurs is not clear.
The name Podostemum comatum was based on the collections of Rodriguez 791 from Iguazu Falls (Argentina). It is clear that Hicken (Hicken 1917) viewed P. comatum as a species with dimorphic stems; the first line of his protologue (p. 149) states "Caules duplicis naturere: ... " Hicken's protologue also notes that the flexuous vegetative stems are markedly longer than the floral stems. Based on this character alone it is evident that the holotype in SI and the isotype in S represent mixed collections of P. comatum and P. distichum; the latter does not have dimorphic stems. We have selected the specimen on the left side of Rodriguez 791 in SI as the lectotype (indicated as "A" on the sheet). The large specimen on the central part of the sheet in S (indicated as "A" on the sheet) is an isolectotype. A possible isolectotype is located in BA (cf., Tur 1997), but was not examined by us.
There is also a duplicate of Rodriguez 791 in U. Royen's annotation label on this sheet states "type specimen duplicate of Podostemum comatum Hicken"; however, the specimens on this sheet are all P. distichum. Thus, this duplicate is not an isolectotype.
The mixed specimens that constitute Rodriguez 791 resulted in some confusion. Royen (1954) recognized P. comatum as distinct but did not examine the type material; rather, he reproduced Hicken's (1917) Latin description. Later, Royen and Reitz (1971) did not recognize P. comatum as a distinct species but listed P. comatum as a synonym of P. schenckii Warm. (we consider P. schenckii as synonymous with P. distichum). The decision by Royen and Reitz (1971) would be understandable if they had focused their attention on the specimens of P. distichum on the holotype sheet instead of those of P. comatum.
Royen (1954) based his description of P. dimorphum on a collection from Parana, Brazil (Dusen 16540). We have examined 16 duplicates of this collection. With the Latin description, Royen (1954, p. 259) listed U as the repository for the type of Podostemum dimorphum; however, he listed C as the repository of the type with the English description earlier in the same paper (p. 235). The reference to C is apparently in error. We have not found a corresponding specimen in C, although there are nine duplicates of Dusen 16540 in U. The specimen here designated as the lectotype has Royen's annotation label bearing the word 'typus' in his hand [accession number 449983B; bar code U0007980]. Isolectotypes are located in CM, L-2 sheets, NY, P, S-2 sheets, and U-8 sheets.