Aetanthus alternifolius F.J. Roldán, Carmona, Alzate & J.S. Murillo, 2021

Murillo-Serna, Jhon S., Roldán-Palacio, Francisco J., Carmona-Gallego, Isabel & Alzate, Fernando, 2021, A new species of Aetanthus (Loranthaceae) from Colombia with notes on A. engelsii, Candollea 76 (1), pp. 71-76 : 72-75

Aetanthus alternifolius F.J. Roldán, Carmona, Alzate & J.S. Murillo , sp. nov. ( Fig. 1 , 2 ).

Holotypus: COLOMBIA. Dept. Santander: municipality of California, [7º22'16” 72º55'29”], 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).

Figures

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.

Fig.2. – Geographical localization of Aetanthus alternifolius F.J. Roldán, Carmona,Alzate & J.S. Murillo (yellow diamond).