NOTAS

Generic identity of Phoradendron rusbyi (Viscaceae) and a new record for Argentina

 

Greta A. Dettke & Jorge L. Waechter

Programa de Pós-Graduação em Botânica, Instituto de Biociências, Av. Bento Gonçalves, 9500 - Bloco IV – Prédio 43433 - sala 205, Universidade Federal do Rio Grande do Sul, Brazil; gretadet@yahoo.com.br (author for correspondence).

---

Abstract.

During a review of herbaria in Argentina we found a specimen of Phoradendron rusbyi, which represents the third collection of the species and a new record for the flora of Argentina. This species is a little aphyllous plant, being a member of the group of hyperparasitic mistletoes, and was found in a mixed collection, parasitizing Phoradendron bathyoryctum. A morphological description of the species is provided, and its inclusion in Phoradendron confirmed.

Keywords. Argentina; flora; mistletoes; Phoradendron; Viscaceae.

Resumen

Durante la revisión de herbarios en la Argentina se encontró un ejemplar de Phoradendron rusbyi, que representa la tercera colección de esta especie y una nueva cita para la flora de este país. Esta especie es una planta pequeña y áfila, miembro del grupo de hiperparásitas, que fue encontrada en una colección mixta, parasitando Phoradendron bathyoryctum. Se incluye una descripción morfológica de la especie y se confirma su inclusión en el género Phorandendron.

Palabras clave. Argentina; flora; hiperparásitas; Phoradendron; Viscaceae.

---

 

INTRODUCTION

Phoradendron Nutt. was first revised for the Argentinean flora in the important work of Abbiatti (1946) which included 12 species for this country. Later, Rizzini & Ulibarri (1986) described a new species named Phoradendron burkartii Rizz. & Ulib., which is now a synonym of P. reductum Trel (Kuijt, 2003). Zuloaga & Morrone (1999) reported 13 species, and more recently Kuijt (2003, 2008) emphasized the occurrence of 14 species of Phoradendron in Argentina.
During a review of herbaria in Argentina we found one additional species, Phoradendron rusbyi Britton, which represents the third collection of this species, formerly known from Peru and Bolivia, and now a new record for the flora of Argentina.

RESULTS

Phoradendron rusbyi Britton, Bull. Torrey Bot. Club 27: 136. 1900. Dendrophthora rusbyi (Britton) Trelease, Phoradendron 218. 1916. TYPE: Bolivia, La Paz, Mapiri, 5,000 ft, IV-1886, Rusby 1543 (lectotype US! designated by Kuijt, Novon 4: 116. 1994; duplicate NY!). Figs. 1-2.

Fig. 1. Phoradendron rusbyi. A, habit. B, detail of young floriferous internode. C, detail of inflorescence in fruit. AC, from Kiesling et al. 8155 (SI). Drawn by E.L.C. Soares.

Fig. 2. Collections of Phoradendron rusbyi from South America.

Plants percurrent, green, erect, up to 15 cm, monoecious. Stem compressed in the distal region (cuneate), internodes short, 1-4 cm; basal cataphylls absent. Leaves absent. Inflorescences lateral and terminal, with one sterile basal internode and 3-4 floriferous segments, each at least 3 cm long, clavate in fruit, each flower area with ca. 20 flowers, triseriate, the three apical staminate flowers with bilocular anthers. Fruits globose, ca. 3 mm in diameter, pearly white, pericarp smooth, petals closed in the fruiting stage.

Distribution and habitat. Phoradendron rusbyi occurs in the eastern slopes of the Andean forest. The small size of the plant makes easy to be it overlooked among the host foliage. The species occurs in the forest canopy, as several other Phoradendron species, making a visual recognition rather difficult.
This new record increases to fifteen the listed species of Phoradendron in Argentina: Phoradendron argentinum Urb., P. bathyoryctum Eichl., P. coriaceum Mart., P. dipterum Eichl., P. falcifrons (Hook. & Arn.) Eichl., P. interruptum (DC.) B.D. Jackson, P. liga (Gillies ex Hook. et Arn.) Eichl., P. mucronatum (DC.) Krug & Urb., P. obtusissimum (Miq.) Eichl., P. reductum Trel., P. rusbyi Britton, P. quadrangulare (Kunth) Griseb., P. paraguari Kuijt, P. piperoides (Kunth) Trel. and P. tucumanense Urb.

Observations. Phoradendron rusbyi was first described as a leafy plant with a 5-nerved leaves, which were later verified by Kuijt (1994) as belonging to its host Phoradendron crassifolium (Pohl ex DC.) Eichl. Trelease (1916) placed P. rusbyi in Dendrophthora Eichler, but did not provide a justification for this change. Phoradendron and Dendrophthora are very similar in their general morphology and the only consistent feature that separates them is the number of anther locules: two in Phoradendron and one in Dendrophthora. The two collections cited by Kuijt (2003), the type from Bolivia and a second collection from Peru [Woytkowski 5740b (US)], have no staminate flowers to confirm the generic identity of this taxon. Kuijt (2003), notwithstanding the absence of basal cataphylls, kept the species in the genus Phoradendron. In the Argentinean material it was possible to verify three staminate flowers on the apical position of floriferous internodes (Fig. 1B) of the young inflorescences of P. rusbyi. The bilocular anthers confirmed the placement of the species in the genus Phoradendron.
According to Kuijt (2003), P. rusbyi is a member of the P. dipterum alliance that includes the leafy P. dipterum and four aphyllous species (P. iltisiorum, P. aequatoris, P. fasciculatum and P. falcatum), all hyperparasitic plants with triseriate inflorescences. All species share the formation of multiple shoots from a basal cushion, as does P. rusbyi (Fig. 1A).
The Argentinean specimen differs from the other two existing specimens by the larger number of flowers and by the clavate segments in fruiting plants. We believe this is a variation within the species, dependent on the degree of fruit maturation. Phoradendron dipterum also shows this variation, showing clavate segments when the fruits ripen sequentially (from the apex to the base of the segment) or nonclavate segments when the ripening of fruits is temporally irregular.

Examined material

ARGENTINA. Jujuy. Depto. Ledesma, entre la Mendieta y San Pedro, 11-XI-1992 (fl, fr), Kiesling, Tur & Ulibarri 8155 (SI 41374).

ACKNOWLEDGMENTS

Our sincere thanks to the researchers of the Instituto de Botánica Darwinion, who facilitated our access to Herbarium SI, and to Manuel J. Belgrano and Norma B. Deginani for their special attention and kindness. This is publication 2 in the Parasitic Plants Research Group technical series.

BIBLIOGRAFÍA

1. Abbiatti, D. 1946. Las Lorantáceas argentinas. Revista del Museo de La Plata, Botánica 28: 1-110.         [ Links ]

2. Kuijt, J. 1994. A hyperparasite mistaken for an inflorescence: The identity and typification of Phoradendron rusbyi Britton (Viscaceae). Novon 4: 116-118.         [ Links ]

3. Kuijt, J. 2003. Monograph of Phoradendron. Systematic Botany Monographs 66: 1-643.         [ Links ]

4. Kuijt, J. 2008. Viscaceae, in F. O. Zuloaga, O. Morrone & M. J. Belgrano (eds.), Catálogo de las plantas vasculares del Cono Sur (Argentina, Sur de Brasil, Chile, Paraguay y Uruguay), vol. 3, pp. 3169-3172. Missouri: Missouri Botanical Garden Press.         [ Links ]

5. Rizzini, C.T. & E.A. Ulibarri. 1986. Phoradendron burkartii Rizz. et Ulib. nueva especie de Loranthaceae. Darwiniana 27: 499-501.         [ Links ]

6. Trelease, W. 1916. The genus Phoradendron. A monographic revision. Urbana: University of Illinois.         [ Links ]

7. Zuloaga, F. O. & O. Morrone (eds.). 1999. Catálogo de las plantas vasculares de la República Argentina. II. Dicotyledonae, vol. 2. Saint Louis: Missouri Botanical Garden Press.         [ Links ]