Murillo-Serna, J.S., F.J. Roldán-Palacio, I. Carmona-Gallego & F. Alzate (2021). A new species of Aetanthus (Loranthaceae) from Colombia with notes on A. engelsii. Candollea 76: 71–76. In English, English and Spanish abstracts.
Aetanthus alternifolius F.J. Roldán, Carmona, Alzate & J.S. Murillo (Loranthaceae) is newly described and illustrated from the department of Santander in northeastern Colombia. This new mistletoe species, known only from the type locality, is discriminate by its indeterminate shoots, alternate or subopposite, obovate leaves, cymose inflorescences bearing three dyads, flower buds c. 9 cm long, with a finely toothed and sometimes fissured calyculus. Its morphological affinities are discussed especially in relation to A. colombianus A.C. Smith and A. coriaceus Patsch. The rediscovery of original material in P of the poorly known Phyllostephanus engelsii Tiegh. (≡ Aetanthus engelsii (Tiegh.) Engl.) is discussed. An emended description is provided and a lectotype is designated. An identification key to the ten species of Aetanthus (Eichler) Engl. occurring in Colombia is also presented.
Introduction
Aetanthus (Eichler) Engl. (Loranthaceae) is a genus of 17 species distributed in the Sierra Nevada de Santa Marta (Colombia) and the Andes of Colombia, Ecuador, Peru and Venezuela between 2000 to 4000 m (Kuijt, 2014; Kuijt & Hansen, 2015). Colombia is the most species-rich country of this genus with ten known species: A. alternifolius F.J. Roldán, Carmona, Alzate & J.S. Murillo, A. colombianus A.C. Smith, A. engelsii (Tiegh.) Engl., A. megaphyllus Kuijt, A. mutisii (Kunth) Engl., A. nodosus (Desr.) Engl., A. ovalis Rusby, A. sessilifolius Kuijt, A. trifolius Kuijt and A. validus Kuijt (Kuijt, 2014; Dueñas, 2020). The region with the most species richness in Colombia is the northern part of the eastern Cordillera. Aetanthus alternifolius, A. colombianus, A. megaphyllus, A. mutisii and A. validus are endemic from this region. Aetanthus nodosus is widely distributed in Central and Western Cordillera, A. ovalis has been reported only from the Sierra Nevada of Santa Marta and A. sessilifolius is known only from the department of Antioquia, where A. trifolius, a species originally described from Venezuela, is also reported (Kuijt, 2014).
Aetanthus is distinguishable from other Loranthaceae genera by its isomorphic stamens and its needle-shaped, basifixed anthers, forming a direct continuation of the filament (Kuijt, 2009, 2014). Phylogenetic analyses place Aetanthus as the sister genus of Psittacanthus Mart., both belonging to tribe Psittacanthinae Engl. (Vidal-Rusell & Nickrent, 2008; Nickrent et al., 2010; Kuijt, 2009, 2014). The two genera differ morphologically by the anther structure: Psittacanthus has versatile, dorsifixed anthers with a blunt apex and Aetanthus has basifixed anthers with a needle-shaped apex (Eichler, 1868; Kuijt, 2009, 2014).
A review of Aetanthus specimens allowed us to find a collection deposited in HUA (Hinestroza et al. 182) that did not match any currently known species. Nomenclatural types and representative specimens were examined through visits to COAH, COL, HUAZ, JAUM, MEDEL and UDBC Colombian herbaria. Other herbaria were consulted through JSTOR Global Plants website [ http://plants.jstor.org/search?plant] and in F, G, GH, K, NY, P, S and US virtual herbaria. We therefore describe and illustrate here the new species Aetanthus alternifolius F.J. Roldán, Carmona, Alzate & J.S. Murillo.
Rediscovery of original material of Phyllostephanus engelsii Tiegh. (≡ Aetanthus engelsii (Tiegh.) Engl.) in P, allowed us to provide an emended description of this poorly known species not included in Kuijt (2014)'s monograph of the genus Aetanthus. Its taxonomic status is discussed and a lectotype is designated. A breakdown of diagnostic characters of the genus is also discussed and an identification key to the species known from Colombia is provided.
Key to the Colombian species of Aetanthus
Adapted from Kuijt (2014)
1. Shoots determinate (each aborting internode forming sympodia) 2
1a. Shoots indeterminate (at least three internodes per innovation) 8
2. Leaves whorled in mature stems (3 or 4 per node) 3
2a. Leaves paired in mature stems 6
3. Leaves in whorls of 4 A. engelsii
3a. Leaves in whorls of 3 4
4. Leaves orbicular to obovate; plants from the Sierra Nevada de Santa Marta A.ovalis
4a. Leaves ovate to lanceolate; plants occurring in the Andes 5
5. Leaves lanceolate, ovate or ovate-lanceolate, thin. Secondary venation inconspicuous and not pronounced; anthers c. 15 mm long A. trifolius
5a. Leaves ovate, thickened. Secondary venation conspicuous and pronounced; anthers c. 10 mm long A. validus
6. Inflorescence a triple dyad A. megaphyllus
6a. Inflorescence a double dyad 7
7. Leaves sessile A. sessilifolius
7a. Leaves petiolate A. nodosus
8. Leaves alternate or subopposite A. alternifolius
8a. Leaves whorled (3 per node) 9
9. Flowers > 15 cm long; calyculus strikingly dentate; terete young stems A. mutisii
9a. Flowers up to 10 cm long; calyculus smooth or finely dentate; young stems 3-ridged A. colombianus
Taxonomy
Aetanthus alternifolius F.J. Roldán, Carmona, Alzate & J.S. Murillo, sp. nov. (Fig. 1, 2).
Holotypus: Colombia. Dept. Santander: municipality of California, [7°22'16” 72°55'29”], 2450 m, 25.I.2013, fl., Hinestroza et al. 182 (HUA-191735!).
Aetanthus alternifolius F.J. Roldán, Carmona, Alzate & J.S. Murillo differs from all other Aetanthus species by the combination of a percurrent habit with indeterminate, slightly flattened shoots without angles, soon becoming terete, subopposite or alternate obovate leaves, cymose inflorescences composed by three dyads, and flowers c. 9 cm long. with a finely toothed and sometimes fissured calyculus.
Hemiparasitic plant, branch parasite. Shoots indeterminate, glabrous, black when dried with whitish lenticels. Internodes 0.7–4 × 0.3–0.5 cm, slightly flattened when young, soon becoming terete, without angles. Nodes not swollen. Haustorium unknown. Leaves subopposite or alternate; leaf blade 4–7 × 2–4 cm, coriaceous, glabrous in both sides, margin entire, obovate, apex obtuse-rounded, base attenuate-cuneate; petioles 2.5–5 × c. 2 mm; venation pinnate, inconspicuous. Inflorescence triple dyads, pendulous, inserted in corky areas 3–6 mm in diameter, conspicuous and adjacent to leaf scars or leaf axils, glabrous, without bracts; inflorescence peduncle c. 6 × 1 mm, dyad peduncles c. 5 × 1 mm, crateriform pedicels, c. 6 mm long (without including the cupular portion), cupules c. 1 × 3 mm. Flowers tubular, red, glabrous; flower buds straight, c. 9 cm long and c. 1 mm in diameter in proximal portions, c. 2 mm in diameter towards distal portion; 6-merous, petals isomorphic, recurved distally in anthesis, medial and proximal portion remain intact. Androecium epipetalous, anthers isomorphic, 14–15 mm long, basifixed, needle-like, 4-loculed. Ovary 4 × 2 mm, cylindrical; calyculus conspicuous, slightly toothed, sometimes fissured; style c. 9 cm long, 0.2–0.3 mm in diameter in proximal portion; stigma 0.3–0.5 mm in diameter, linear, inconspicuous, continuing as an extension of the style. Fruits not seen.
Etymology. – The epithet alternifolius refers to the phyllotaxy in mature shoots.
Distribution and habitat. – Aetanthus alternifolius is known only from a single specimen collected in the municipality of California, in montane oak (Quercus humboldtii Bonpl.) forests belonging to the surrounding area of the Páramo de Santurbán (Santander, Colombia) close to 2800 m. Host is unknown for this species.
Phenology. – This species was collected with several inflorescences in anthesis and flower buds at the end of January. Fruits remain unknown.
Conservation status. – Aetanthus alternifolius occurs in montane oak forests that are severely threatened by mining and agricultural activities (Avella & Rangel, 2014). Nevertheless, additional studies are required for this mistletoe, especially regarding its host range, distribution and ecology. We suggest considering this species as “Data Deficient” [DD], according to the IUCN Red List Categories and Criteria (IUCN, 2012), awaiting the results of new studies. Notes. – Species of the genus Aetanthus display a series of diagnostic characters that are useful to determine taxa at species level. Some of those are: ramification pattern (percurrent or indeterminate vs. aborted terminally or determinate); phyllotaxy (opposite-decussate or whorled), number of dyads per inflorescence and flower length. Some features are unique among Aetanthus species, as a strikingly dentate calyculus in A. mutisii, sessile leaves in A. sessilifolius (Kuijt, 2014) and the alternate phyllotaxy observed in A. alternifolius.
Aetanthus alternifolius has morphological affinities with A. colombianus and A. coriaceus, displaying similarities in growth habit and flower length. However, these three species can be distinguished by their phyllotaxy, inflorescence structure and stem shape. Most relevant characters to discriminate the three species are presented in Table 1.
Aetanthus alternifolius occurs sympatrically in the Central Cordillera, along with three additional species of the genus, which can be differentiated by the following morphological characters: A. megaphyllus has dichotomous branching and greater sized leaves with stout leaf blades and petioles; A. validus exhibits a dichotomous ramification with 3-whorled leaves and A. mutisii has a percurrent habit, whorled phyllotaxy and flowers ranging 15–22 cm long with a strikingly dentate calyculus.
Kuijt (2009, 2014) reports that it is common that Loranthaceae taxa are known only from a few localities and usually, taxonomic novelties are published based on a single gathering. This may be due to habit-imposed difficulties and collectors' taxonomic interests (Cavallin et al., 2016).
Fig. 1.
Aetanthus alternifolius F.J. Roldán, Carmona, Alzate & J.S. Murillo. A. Habit; B. Inflorescence; C. Detail of anther and filament union; D. Stigmatic region detail.
[Hinestroza et al. 182, HUA] [Drawings: D. Zapata]
Fig. 2.
Geographical localization of Aetanthus alternifolius F.J. Roldán, Carmona, Alzate & J.S. Murillo (yellow diamond).
Notes on Aetanthus engelsii
Aetanthus engelsii (Tiegh.) Engl. in Engl. & Prantl, Nat. Pflanzenfam., Nachtr. 1: 136. 1897.
Phyllostephanus engelsii Tiegh. in Bull. Soc. Bot. France 42: 358. 1895.
Lectotypus (designated here): Colombia: sine loco, s.d., Engels s.n. (P [P05066078] image!; isolecto-: P [P05066079] image!).
Hemiparasitic plant, branch parasite. Shoots determinate, each innovation aborting terminally, tetratomic branching, glabrous. Internodes 3–15.5 × 0.2–0.5 cm. Nodes slightly swollen. Haustorium unknown. Leaves 4-whorled; leaf blade 2.5–11 × 2–6 cm, coriaceous, glabrous in both sides, margin entire, elliptic, apex obtuse-rounded, base attenuate-cuneate; petioles 3–5 × c. 2 mm; venation camptodromous, visible. Inflorescence unknown. Flowers tubular, glabrous; flower buds straight, up to 10 cm long. Androecium epipetalous, anthers isomorphic, c. 9 mm long, basifixed, needle-like. Ovary c. 3 × 2 mm, cylindrical; calyculus conspicuous, smooth to sinuate. Fruits unknown.
Notes. – Van Tieghem (1895) described Phyllostephanus engelsii based on a collection by M. Engels in Colombia. Two sheets of original material have been located in P [P05066078, P05066079]. We designate here the specimen [P05066078] as lectotype, because it is the best preserved and most complete sheet including leaves, branches and flowers.
The precise geographic location of the type gathering is uncertain only refering to Colombia. The protologue was also very succinct just mentioning A. engelsii has 4-whorled leaves and tetratomic branching (Van Tieghem, 1895).
Aetanthus engelsii, with 4-whorled leaves and determinate shoots resembles A. prolongatus Kuijt, but it has dichotomous branching (vs. tetratomic in A. engelsii). Additionally, A. prolongatus is endemic to the Venezuelan Andes (Kuijt, 2014). Aetanthus tachirensis Kuijt also has 4-whorled leaves but differs by its obscure venation pattern (vs. visible leaf veins in A. engelsii) and indeterminate shoots (vs. determinate in A. engelsii).
Table 1.
Distinctive characters between Aetanthus alternifolius F.J. Roldán, Carmona, Alzate & J.S. Murillo, A. colombianus A.C. Smith and A. coriaceus Patsch.
Acknowledgments
The authors would like to thank Diego Zapata for the illustration of the specimen and staff from COAH, COL, HUA, HUAZ, JAUM, MEDEL and UDBC herbaria for allowing the use of equipment and granting access to the collection. We would like to thank Claudenir Simões Caires for his review of the manuscript, Peter B. Phillipson for the photographs from the inside of the fragment packets in P and Martin W. Callmander for his editing, comments, and effort that greatly improved this article.
