Danaea iridescens Christenh.

Christenhusz, Maarten J. M., 2024, A new species of the fern genus Danaea (Marattiaceae) in the Greater Antilles, Phytotaxa 650 (3), pp. 291-296 : 291-294

Danaea iridescens Christenh. , sp. nov. ( Fig. 1 )

Type:— PUERTO RICO. Cordillera Central, Toro Negro , Cerro Doña Juana , steep SE slope on lateritic clay, 18° 10’N, 66° 29 W, 1031 m, 9 March 2004, Christenhusz & Kolterman 3487 (holotype MAPR!, isotype TUR!).

This species belongs to subgenus Danaea in having creeping, bifacial rhizomes and petioles without nodes. It is similar to D. grandifolia in having entire pinna apices and broad pinnae, but the new species is geographically isolated from D. grandifolia and retains its iridescent sheen in adulthood, which is not the case in Colombian D. grandifolia , which is dark green in adulthood (pers. obs. 2017, Fig. 2 ; see vouchers Madriñán & Christenhusz 7774 (JBGP!), 7822 (JBGP!) and 7872 (PG-0194!). It differs from D. nodosa , which also occurs on Puerto Rico and Hispaniola, but at lower elevations, in its entire pinna apices. It also differs from the Mesoamerican D. media which has acuminate-caudate apices and oblanceolate pinnae that are widest above the middle. The only other species that is (usually) metallic iridescent in adulthood is D. leussinkiana from Costa Rica, but this has simple unbranched veins that are rarely paired.

Large ferns to 2 m tall, with arching fronds and massive creeping rhizomes, in habit somewhat resembling a small, prostrate palm. Rhizomes creeping-ascending, radially arranged, but roots all on the lower side, to 50 cm long, 10 cm wide at apex when fresh, 3–6 cm wide when dry; stipules 1.5–2.5 cm wide; leaves imparipinnate; adult sterile leaves (79–) 143–165 cm (most specimens in herbaria are either juvenile or leaves are young, often only parts of adult leaves are preserved), petioles (38–) 72–80 cm long, without nodes; rachis winged in the upper two internodes, the wing to 1 mm wide, sparsely scaly at nodes, scaly on the midrib below; blades concolorous, dark green, blue-iridescent, (41–)68–85 × 50–65 cm, with 10–12 pinna pairs, the basal pinnae petiolulate; largest lateral pinnae (ob)lanceolate, about six times longer than wide, 19–38 × 3.0– 5.7 cm, widest at or above the middle, apices acuminate, bases acute, margins entire, sometimes slightly sinuate apex; terminal pinnae present, lanceolate, 15–30 × 3.3–6.0 cm, parallel-sided, margins entire; veins usually paired at base or occasionally forked, 10–14 veins per cm; fertile leaves 151–153 cm long, possibly longer, petioles 83 cm long without nodes, blades 68 × 40–52 cm with 10–12 pinna pairs, possibly more; lateral pinnae ovate-lanceolate, about six times longer than wide; largest lateral pinnae (14–)16–25 × 2.1–4.2 cm, widest below the middle, apices acuminate, sterile at ultimate tip, bases obtuse, margins entire with a sterile margin of 0.5 mm wide; terminal pinnae present, ovate-lanceolate, (10.0–)13.0– 19.5 × 1.8–2.7 cm, widest below the middle, margins entire; juveniles a single pinna pair when the leaves 10 cm long, the second pair appearing when 22 cm long. ( Fig. 1 )

Distribution:—This species is only found on the Greater Antillean islands of Puerto Rico and Hispaniola, usually at elevations above 900 m.

Ecology:—These are terrestrial ferns with a strong mycorrhizal relationship. They grow in thick humus over loam or clay in moist shade under closed canopy forest, often in deep shade under boulders ( Fig. 1 ).

Specimens examined (paratypes):— HAITI. Massif des Cahos, gr. Las Caobas, Morne Dos-Bois-Rouge, Ekman H 5551 ( C!, K!). DOMINICAN REPUBLIC. LA VEGA: Dense moist ravine with rivulet in Loma entre Los Ríos between La Ciénega and Los Tablones, Gastony et al. 387A ( GH!) ; BARAHONA: E edge of Sierra de Baoruco, 22.5 km road SW of Barahona, 9.4 km W of El Arroyo at Las Filipinas, Michel et al. 9003 ( NY!). MONTE CRISTI: Distr. of Sabaneta, Las Cidras , Valeur 526 ( C!, F!, K!, MO!, P!). PUERTO RICO. Monte Guillarte, Christenhusz 3493 ( MAPR!, TUR!, UPRRP!) ; Toro Negro, Cerro Doña Juana , Christenhusz & Kolterman 3487 ( MAPR!, TUR!) ; Christenhusz & Kolterman 3505 ( TUR!, MAPR!) ; Toro Negro, Camino El Bolo, Christenhusz & Kolterman 3507 ( MAPR!, TUR!) ; Cerro Roncador, Christenhusz et al. 4230 ( BM!- BM 000823532, BM 000823533, TUR!, UPR!) ; Arroyo de Los Corchos between Adjuntas and Jajuya, Britton et al. 5241 ( F!, P-00251820!, NY!) ; Utuado, Sintenis 6333 ( P!- P 00251774) .

Etymology:—This species has an iridescent metallic sheen, even when adult. The name thus refers to the iridescence of the plant when fresh. Unfortunately, this character disappears when dried.

Figures

FIGURE 1. Danaea iridescens in Toro Negro, Puerto Rico, USA, 2004. Photograph by Maarten Christenhusz.

FIGURE 2. Danaea grandifolia in Santa Marta, Colombia, 2017. Photograph by Maarten Christenhusz.