Podostemum irgangii C. T. Philbrick & A. Novelo, Novon 11: 92. 2001.-TYPE: BRAZIL. Santa Catarina: Abelardo Luz, "Quedad do Rio Chapeco," a series of waterfalls located ca. 5 km W of the city of Abelardo Luz, 13 Jan 1999, Philbrick, Novelo, Irgang & de Senna 5466A (holotype: ICN!; isotypes: MEXU! MO! NY! WCSU!). Plant Description:
Roots 0.2-2.1 (0.9) mm wide. Stems monomorphic, arising 0.2-20 (4.3) mm apart along roots, erect, 1-42 (20) mm long. Leaves petiolate, arising perpendicular to the stem axis or reflexed, arising in ca. 180° distichous arrangement, with a central axis from which arise leaflets in a verticillate manner, 3.1-7.2 (5.2) mm long; leaf divisions arising in a 3-dimensional manner, with 5-14 (8) verticils per leaf, 6-11 (9) leaflets per verticil, distance between verticils 0.3-0.6 (1.5) mm; ultimate leaf segments 0.2-0.9 (0.6) mm long, awl-shaped, parallel-margined or triangular, rounded to triangular in cross section, incurved, apices acute; petioles 0.2-0.4 (0.3) mm long, round to elliptical in cross section; leaf bases symmetrical, attached perpendicular to stem axis, rigid; stipules of two forms, both types rigid, symmetrical, persisting, becoming hardened and darkened on older por tions of the stem: 1) 2 auriculate, lobed or unlobed segments detached from the leaf base, on either side of the petiole base, perpendicular to the stem axis, or at an angle of up to a 45° relative to the stem axis, 0.7-1.1 (1) mm wide, projecting 0.4-0.6 (0.5) mm from stem; 2) 3-9 (4) upright, finger-like structures traversing the adaxial side of the petiole adjacent to the stem, 0.2-0.5 mm (0.4) long, blunt. Flowers 1-7 (1) per stem, spathella 2.3-3 (2.4) mm long, 1.1-2.1 (1.5) mm wide, smooth to papillate, apex rounded or minutely cleft, with an apical ridge, cap-like apical portion becoming reflexed after spathella rupture; tepals 3, linear or awl-shaped, straight or curved, apex acute; lateral tepals 0.6--1.9 (1.2) mm long; andropodial tepal 0.4-1.5 (1) mm long; andropodium 0.3-1.7 (1) mm long prior to anthe sis, during anthesis to 2.2-4.6 (3.4) mm; stamens 2; filaments 0.3-1.2 (0.5) mm long prior to anthesis, during anthesis to 1.1-1.7 (1.6) mm; anthers 0.8-2.1 (1.3) mm long, 0.7-1.3 (0.8) mm wide; pollen dyads 27-40 (35) µm long, 20-25 (23) µm wide; ovary 0.6--2.1 (1.4) mm long, 0.8-1.6 (1.1) mm wide; stigmas entire, 0.4-1.4 (0.6) mm long prior to anthesis, during anthesis to 0.9-1.6 (1.2) mm; pedicels 0.3-3.1 (1) mm long prior to anthesis, dur ing anthesis to 0.6--5 (2.4) mm. Capsules 1.2-2.2 (1.6) mm long, 0.9-1.7 (1.2) mm wide; 6 ribbed (3 per valve), suture margins also rib-like; pedicels in fruit 1-6 (2.4) mm long; seeds 2-70 (38) per capsule, 0.2-0.4 (0.3) mm long, 0.1-0.3 (0.2) mm wide.
Distribution: Brazil (south-central Parana and central to western Santa Catarina); locally abundant, forming dense growths on horizontal to vertical rock surfaces; 618-1000 m.
Podostemum irgangii has been observed growing with P. distichum, P. muelleri, P. rutifolium subsp. rutifolium, and Tristicha trifaria.
ADDITIONAL SPECIMENS EXAMINED. Brazil. PARANA: Rio Canto Galo, Laranjeiras do Sul, Hatschbach 19182 (K, US); 20kmN oflratim, on rocks in brook, General Carneiro, Smith et al.15714 (US).-SANTACATA RINA: Rio Chapecozinbo, Cascata Manela, Xanxere, Philbrick et al. 5441, 5449, 5450 (ICN, MEXU, WCSU); Rio Chapec6, locality called Prainha, 10-15 km E of Abelardo Luz, Philbrick et al. 5456-5459 (ICN, MEXU, WCSU); Rio Chapeco, Quedad do Rio Chapeco, ca. 5 km W of Abelardo, Philbrick et al. 5464, 5466A, 5472 (ICN, MEXU, WCSU); along BR-282, near town of Ponte Serrana, Philbrick et al. 5473, 5474 (ICN, MEXU, WCSU); Rio Chapeco, Abelardo Luz, Smith & Klein 13892 (B, NY, R, US); Campo de Irani, Irani, Smith & Klein 13992 (US); Rio Irani, 23 km E of Ponte Serrada, Joacaba, Smith & Reitz, 9888 (L, R, US); 2 km W of Rio Capetinga, Dionisio Cerqueira, Smith et al. 9619 (K, L, R, US).
Podostemum irgangii is the only species in the genus with dimorphic stipules. Both stipule types are firm when young, become hardened and blackened several nodes below the stem apex, and generally persist after the leaves have fallen away.
The narrowly distributed P. irgangii is similar to P. distichum, a widespread and mor phologically variable species. Phylogenetic analyses (see above) indicate that they are sis ter species. The two are distinguished readily based on stipule features when actively growing or from senesced vegetative specimens. Podostemum distichum has a boat shaped sheathing leaf base, with the apex divided into two to six prominent triangular, flattened stipular teeth.
Leaf form generally differs between P. distichum and P. irgangii, but can overlap in some populations. Both species have divided leaves. The leaves of P. distichum are highly variable. Leaf segments can be irregularly arranged, subdichotomous, dichotomous, semi-verticillate (a central rachis from which irregularly placed leaflets arise), or (rarely) verticillate. When semi-verticillate or verticillate, there are two or three primary axes on the leaf. In contrast, leaves of P. irgangii have a single primary axis, are uniformly verti cillate, and are composed of a central rachis from which whorls of leaf segments arise. Leaves of P. irgangii sometimes have a rudimentary secondary axis on the abaxial side of the petiole base.