Cyathea ruttenbergii, Tejedor, Adrian & Areces-Berazain, Fabiola, 2018

Tejedor, Adrian & Areces-Berazain, Fabiola, 2018, Cyathea ruttenbergii, a new tree fern (Cyatheaceae, Polypodiopsida) from Puerto Rico, Phytotaxa 336 (3), pp. 279-285 : 280-283

Cyathea ruttenbergii A. Tejedor and F. Areces sp. nov.

Type:— PUERTO RICO. Río Grande: El Yunque National Forest, route 191, km. 4.8, 210 m, 18.33777, -65.763647, 30 July 2017, F. Areces 1160 (holotype: UPRRP!, isotype NY!). Figs. 1, 2 (A, D, G).

A new exindusiate Cyathea similar to Cyathea borinquena but differing in its erect trunk, fountain-like crown architecture, bicolorous petiole scales, denser petiole scurf, wide sinuses, and crenulate segment margins.

Trunks erect to decumbent, to 2 m tall, 5–7 cm diam., covered with old petiole bases, sparsely covered with bicolorous reddish brown scales with lighter margins, similar to petiole scales; apex hidden between petiole bases, these inserted at a high angle and forming a tight fascicle. Fronds to 190 cm long, first ascending then slightly arching, forming a fountain-like crown. Petioles to 60 cm long, strongly armed with short, basally wide, stout spines to 6 mm long, bright green adaxially and atropurpureous to blackish abaxially, matte, with moderately dense scurf consisting of matted arachnoid squamules, irregular light brown squamules, and tortuous hairs to 1.0 mm long, petioles on each side with a discontinuous line of overlapping orange-brown lenticels to 4.0 × 0.8–1.0 mm, scaly along basal third in young petioles, most scales soon caduceous and retained only at base in older petioles. Petiole scales ovate-lanceolate, 10.0–15.0 × 4.0–5.0 mm, shiny, concordantly bicolorous brown with lighter translucent yellowish to cream margins, apices darkened, bases lighter and weakly cordate, apices attenuate, sinuous; differentiated margins fragile, often abraded, the cell rows strongly exerted. Laminae to 90 × 70 cm, broadly ovate, bipinnate-pinnatifid, chartaceous, shiny, a rich green adaxially, paler abaxially; 6–7 pinna pairs, basal ones strongly reflexed ca. 1/2 the length of the longest pinnae; apices abruptly reduced. Frond axes muricate, light green to pale reddish brown when older, brown to atropurpureous abaxially, matte to weakly shiny, adaxially pubescent with thin whitish tortuous multicellular hairs to 1.0 mm long, hardly contrasting with green epidermis, abaxially with similar but denser indument, more strongly contrasting with atropurpureous epidermis; costae to 3.0 mm, junctures of costae and rachises abaxially swollen, each with only one large, conspicuous, weakly protruding elliptic aerophore to 6.0 × 2.5 mm, pale brown. Pinnae to 45 cm long, ascending, stalked to 2.5 cm, alternate, articulate, distally weakly to green-alate, ending in a pinnatifid apical section. Pinnules to 12 × 2.5 cm, stalked to 4 mm, inarticulate, 2–3 cm between the stalks, elliptic-lanceolate, bases asymmetric, with a gap or missing segment on distal margin of stalk, tips attenuate with crenulate margins; costules green on both sides, abaxially strongly prominent, ridged, with sparse tortuous white hairs to 1 mm and flat, lanceolate whitish to beige squamules to 1.5 mm. Segments to 15 × 6 mm, sessile, adnate, ascending, falcate, tips acute, alternate, proximal segments shorter than following segments, basal segments strongly asymmetric, if remote then connected by wide green wing; sinuses oblong to acute to 3.0 mm wide, never occluded; margins crenulate; midveins with few, tortuous, white hairs to 1 mm; veins simple or forked, protruding abaxially, green, ending at the margins, glabrous to glabrescent on both sides, with flat, whitish lanceolate squamules to 1.0 mm, and beige to pale brown sub-bullate squamules. Sori 1.0– 1.2 mm diam., supramedial to submarginal at segment base, more or less parallel to margins, in the fork or on the back of veins; indusia lacking; receptacles globose, 0.3–0.4 mm diam., paraphyses few, hyaline, much shorter than the sporangia. Spores not examined.

FIGure 1. Cyathea ruttenbergii (A–D, from F. Areces 1160 UPRRP). A. Fertile pinna, silhouette. B. Fertile segment, abaxially. C. Petiole scale. D. Fertile pinnule, abaxially. E. Cyathea pungens , fertile pinnule, abaxially (from field photograph by AT). F. Cyathea aspera , fertile pinnule, abaxially (from Axelrod 15979 UPRRP). G. Cyathea borinquena , fertile pinnule, abaxially (from field photograph by AT).

Other specimens examined:— PUERTO RICO. Luquillo: Caribbean National Forest, Road 968 to Barrio Sabana, 800 ft, 25 June 1966, Woodbury sn ( SJ!). Río Grande: Bo. Mameyes II, El Yunque National Forest, Rt. 191, km 5, roadside in wet mountain forest, 250 m, 25 January 2010, Axelrod 14285 ( UPRRP!). El Yunque National Forest, montane rain forest along roadside, 550 m, 25 January 2010, M. Lehnert 1668 ( UPRRP!). Sierra de Luquillo, Caribbean National Forest, road 988, ca. km 2, 110 m, 28 September 1983, Woodbury sn ( SJ!). Barrio Jimenez, Finca San Pedrito, ca. 0.9 km, due ESE of road 186 at El Verde, 210–240 m, Proctor 50417 ( SJ!). Sierra de Luquillo, Caribbean National Forest, road 191 km 5.5, 460 m, 3 August 1984, Proctor 40657 ( SJ!). Sierra de Luquillo, Caribbean National Forest, road 988 1.4 km SSE of intersection with road 191, 120 m, 23 December 1983, Proctor 39970 ( SJ!). Utuado: Rio Abajo State Forest, ca. 1.6 km WSW of Campamento Crozier 320– 240 m, 13 August 1984, Proctor 40707, 40706 ( SJ!). Bosque de Río Abajo, 250 m, 17 August 1994, C. Sánchez 1873218–1873220 ( NY!).

Etymology:— The epithet honors Kathy Ruttenberg, whose visceral art, love for wild creatures and places, and generous support for the conservation of nature are an inspiration.

Similar species:—All specimens of Cyathea ruttenbergii held at the NY, SJ, and UPRRP herbaria, before the addition of our collections at El Yunque, had been identified as either Cyathea pungens ( Willdenow 1810: 206) Domin (1929: 263) or C. aspera . Cyathea pungens from South America shows indeed an uncanny resemblance to C. ruttenbergii . Both are small-statured forest understory species that share a fountain-like crown architecture, an abruptly reduced frond apex, supramedial placement of sori, stout spines, bicolorous scales, and scales along costules. From C. ruttenbergii , C. pungens differs in its elliptic lamina, with 8–14 pinna pairs and rather decurrent bases, oblong, nearly sessile pinnules with acute to short-attenuate tips, oblong segments with obtuse tips, undulate segment margins, abundant brown bullate squamules along costae, and glabrescent costules. Cyathea ruttenbergii , in contrast, has a broader, more ovate lamina with 6–7 pinna pairs, elliptic-lanceolate pinnules with long attenuate tips, asymmetric pinnule bases, with a gap or missing segment on distal margin of stalk, falcate segments with acuminate tips, crenulate segment margins, lack of bullate squamules along costae, and white tortuous hairs on costules. Contrary to the thick fascicle of petioles that characterizes C. ruttenbergii , C. pungens usually develops a protruding apex not hidden by petiole bases and frequently produces adventitious buds, not observed in C. ruttenbergii .

Cyathea ruttenbergii has also been confused with C. aspera , a Caribbean species that occurs in two somewhat diverging populations throughout the Greater and Lesser Antilles (Lehnert, 2016) but is oddly absent from Puerto Rico. It is distinct from C. ruttenbergii in its relatively oblong pinnules, concolorous brown scales, abundant large, brown bullate squamules along segment midveins, medial sori, and, at least in the Lesser Antillean population, profuse accessory scales subtending the sori that are highly conspicuous after sporangia have been shed. In contrast, C. ruttenbergii has elliptic-lanceolate pinnules, concordantly bicolorous petiole scales with dark brown centers and translucent whitish to cream margins, midveins lacking large bullate squamules, and supramedial sori not subtended by accessory scales.

Among the tree ferns that do occur in Puerto Rico, several species have been found growing in the vicinity of C. ruttenbergii , including C. borinquena , C. horrida ( Linné 1753: 1092) Smith (1793: 416) , and C. arborea ( Linné 1753: 1092) Smith (1793: 417) .Among these species, C. ruttenbergii stands out because of its ascending, fountain-like crown, supported by a short trunk, and by its thick trunk apices formed by a dense fascicle of 10–15 petioles inserted at high angles. Of all sympatric congeners, C. ruttenbergii may be most easily confused in nature with C. borinquena , a Puerto Rican endemic with which it may have the closest phylogenetic affinities based on laminar indument and division and soral characteres. Cyathea borinquena , however, is easily distinguished from C. ruttenbergii by its creeping, rarely erect trunk, remote petiole insertions that do not form a tight fascicle around a protruding trunk apex, sinuous to entire segment margins, narrow sinuses, long pinnule stalks to 15 mm, long lanceolate, concolorous brown scales, scant to absent petiole scurf and weakly developed spines. Cyathea ruttenbergii , in contrast, has a usually erect and rarely decumbent trunk, petioles tightly arranged in fascicle around trunk apex, crenulate segment margins, wide sinuses, short pinnule stalks to 4 mm, ovate, bicolorous scales with dark brown centers and light whitish to cream margins, thicker petiole scurf of arachnoid squamules and tortuous hairs, and stout spines.

Cyathea arborea and C. horrida , two other species of Cyathea that co-occur in nature with C. ruttenbergii , are readily distinguished from C. ruttenbergii by their habit and indusia. Cyathea arborea develops a tall trunk to 10 m that sheds petiole bases cleanly, and has a gradually reduced frond apex and a cyatheoid indusium. Cyathea horrida has a pinnate-pinnatisect lamina and hemitelioid indusium. Cyathea ruttenbergii , in contrast, has much shorter trunks usually to 70 cm and exceptionally to 2 m that retain old petiole bases, laminae that are bipinnate-pinnatisect with abruptly reduced frond apices, and lacks indusia.

Distribution and habitat:— Cyathea ruttenbergii is known only from the Island of Puerto Rico, having been found in scattered lowland localities (100–550 m) of the Luquillo Mountains in the eastern part of the island and at one locality, the Rio Abajo State Forest near the town of Utuado, in the northern limestone belt. All records listed under C. pungens by Proctor (1989) and Axelrod (2011) from the central part of the island represent C. ruttenbergii . The population known to the authors consists of a few dozen individuals occurring both in patches and as isolated plants along route 191, the main public access road from the northern coastal plain to El Yunque National Forest. The plants grow in deeply shaded understory, under tall secondary wet forest. Proctor (1989), under C. pungens , indicates that the species is locally common and occurs in wet, sheltered ravines and borders of wooded swamps.

In the Grater Antilles, Puerto Rico has one of the climates that most closely resemble an equatorial climate. Its eastern location in the archipelago, on the path of the NE trade winds, and surrounded by a warm ocean with stable sea surface temperatures, ensure year round formation of convective clouds and orographic rain ( Proctor 1989). At El Yunque rain forest, on the windward side of the island, mean annual precipitation exceeds 3000 mm (up to 4000 mm at higher elevations) and no month receives less than 100 mm of rain ( Murphy et al., 2017), which rivals the equatorial rainfall regime found along most of the eastern slopes of the Andes from southern Colombia to northern Peru, wellknown for their high tree fern diversity ( Lehnert 2006; Lehnert, 2011; Tejedor, in press; Tejedor and Calatayud, in press). Considering the tight relationship of tree fern species richness with high, stable annual precipitation ( Bystriakova et al., 2011; Tejedor, in press.) it is perhaps not that surprising that an endemic, unnamed species of tree fern in the Caribbean should be found in Puerto Rico.

Note:— Proctor (1989) also lists C. pungens from the island of Hispaniola. It is possible that that population may actually represent C. ruttenbergii . Therefore, further examination of the specimens that form the basis for that record is warranted.