Actinostachys simplex Amoroso & Coritico, 2021

Amoroso, Victor B., Cariño, Yvonne Love L., Nobleza, Joevina C. & Coritico, Fulgent P., 2021, A new species of Actinostachys (Schizaeaceae) from Mindanao, Philippines, Phytotaxa 508 (1), pp. 101-106 : 102-105

Actinostachys simplex Amoroso & Coritico , sp. nov. ( Figures 1 , 2 )

Diagnosis:—This new species Actinostachys is most similar to Actinostachys wagneri (Selling) C.F. Reed (1948: 131) but differs by its consistently single and longer sorophore with glabrous sporangia and distinct and longer stipe.

Type:— PHILIPPINES. Mindanao Island. Davao Oriental. San Isidro Municipality , Mount Hamiguitan Range Wildlife Sanctuary , 455 m, 1 February 2021, VB Amoroso 20312 with JC. Nobleza (holotype: PNH!; isotypes: CMU!) .

Terrestrial. Roots dark, wiry, stiff, ca. 0.1–0.2 mm, branching, covered with long, rigid, brown root hairs, 3–6 per rhizome. Rhizome round to oblong, short-creeping to erect, less than 1 cm in diameter, dark brown outward but yellowish in transection, covered with profuse, long, dark brown coarse glandular hairs which are appressed, longer and narrower than root hairs. Fronds monomorphic, 1–3 per rhizome, erect, linear, grass-like, unbranched, green, up to 18.5 cm long; stipe distinct, 13–15 mm long, dark brown, more or less tetragonal in transection with 1–2 layers of sclerenchymatous epidermal cells and 2–3 cell layers of large cortical cells, vascular tissues reduced, haplostelic, slightly grooved, with short trichome; lamina (sterile portion) simple, narrowly linear up to 6.7–14.5 cm long x 0.5–0.9 mm wide, unbranched, green, abaxial slightly grooved, concave in shape at base becoming turbinate at the middle in transection with thick cuticle and 2–3 layers of thick-walled epidermal and hypodermal cells, margin entire with 2–3 layers of parenchymatous cells, adaxial surface with distinct costa and alternating warty indumentum distantly distributed throughout the lamina; stomata hypocytic, in one row (uniseriate) on each side of the costa, oppositely arranged; sorophore linear, consistently single per frond, terminal, sessile, 10–20 mm long; laminae of sorophores green, glabrous, margin entire and reflexed, apex entire when young becoming bifid when mature; sporangia arranged in 2 rows, alternately arranged, completely covering the abaxial surface and protected by reflexed edge of sorophore lamina, sessile, obovoid, surface striated, glabrous with distal annulus, annular cells 12–14, spores monolete, obovate, striated, size 18–20 x 10–13 µm.

Distribution and Habitat:— This species is currently known only within the buffer zone located outside the boundaries of MHRWS in San Isidro Municipality, in partly shaded habitat in lowland tropical rain forest within ultramafic substrate. It grows terrestrially underneath Gymnostoma rumphianum together with its thick layer of decaying fallen leaves. The vegetation surrounding A. simplex includes Pittosporum pentandrum (Blanco) Merr. (1905: 19) , Greeniopsis megalantha Merr. (1917:164) , Rhodomyrtus surigaoensis Elmer (1914: 2344) and Pandanus sp. The ground cover is dominated by Davallia solida (G.Forst.) Sw. (1801: 87) , Nepenthes mindanaoensis Sh.Kurata (2001: 32) and Dicranopteris linearis (Burm.) Underw. (1907: 250) . Two other species of grass ferns, A. inopinata and Schizaea dichotoma (L.) Sm. (1793: 422) were observed growing near A. simplex .

Additional specimens examined:— Philippines, Mindanao, Davao Oriental, Municipality of Governor Generoso , MHRWS., 6˚27’45.29” N, 126˚10’19.07” E, 115m asl., 26 January 2021, VB Amoroso Collection No. 20289. No fertile fronds were collected .

Etymology:— The specific epithet refers to the consistently simple sorophore.

Suggested Common Name:— Simple Grass Fern.

Notes:— We compare the new species to the three other species of Actinostachys that are most similar to it in morphology based on published descriptions of Amoroso et al. (2020), Holttum (1955), Reed (1947), Lindsay et al. (2012), as well as examinations of JSTOR Type images. Our species is closest morphologically to A. wagneri (Selling) C.F. Reed , followed by A. minuta Amoroso et Coritico , and A. plana (Fourn.) C.F.Reed (1948: 131) ( Table 1). Our new species is strictly terrestrial while the other three species of Actinostachys are epiphytes.

The sterile portion of the lamina of A. wagneri and A. minuta come closest in width to those of A. simplex (0.5–1 mm wide versus 0.5–0.9 mm respectively). Actinostachys simplex is similar to A. wagneri by its sterile lamina and sorophore width and striated spore surface. However, it differs from A. wagneri in having distinct stipe about 13–15 mm long (vs. indistinct), shorter sterile lamina (6.7–14.5 cm long vs. up to 20 cm long), single sorophore (vs. 2–5) and glabrous sporangia (vs. sporangia with brown hairs).

Individuals of A. simplex are terrestrially growing mixed with similar fallen leaves of Gymnostoma rumphianum and are thus highly camouflaged as shown in Fig. 1 . This species is obscure in the field because it resembles grass seedlings and so can be easily passed over by floristic botanists.

Conservation Status:— We observed the restricted population from the type locality in the buffer zone of MHRWS in San Isidro. Its location in the buffer zone and along the foot trail will likely decimate the population of A. simplex . Thus, we recommend listing the species as Critically Endangered ( CR) based on its very small and restricted population, likely continuing decline due to disturbance from the foot trail and an area of occupancy estimated to be <10 km 2 ( IUCN Standard and Petition Committee 2019) .

Key to the Philippine species of Actinostachys

1. Lamina ≥ 2 mm wide; stipe indistinct ................................................................................................................................................2

–. Lamina <2 mm wide; stipe distinct ...................................................................................................................................................3

2. Lamina (sterile portion) ≤ 5 mm wide; stomata in one row on each side of costa; sporangia in four rows on the sorophores ........... ............................................................................................................................................................................................. A. digitata

–. Lamina (sterile portion) ≤ 2.5 mm wide; stomata in two rows on each side of costa; sporangia in two rows on the sorophores ....... ......................................................................................................................................................................................... A. inopinata

3. Epiphytic; sorophore <6 mm long; 1 to 4 but usually 1..................................................................................................... A. minuta

–. Terrestrial; sorophore ≥ 6 mm long; consistently 1............................................................................................................ A. simplex

Figures

FIGURE 1. Habit of Actinostachys simplex Amoroso & Coritico growing in a thick layer of decaying brown needle leaves of Gymnostoma rumphianum (Miq.) L.A.S.Johnson and bearing single sorophore (so) indicated by the arrows.

FIGURE 2. Actinostachys simplex Amoroso & Coritico. A) habit showing distinct stipe (st), narrow lamina (la) and single sessile sorophore (so), B) rhizome with obconic glandular hair (inset) and roots, C) tetragonal stipe in transection, D) grooved lamina with an indumentum in the margin, E) lamina transection showing thick-walled epidermal cells with an undifferentiated mesophyll, F) lamina with a distinct costa (c), G) single row of hypocytic stomata (sm) on each side of the costa, H) sorophore, I) top view of sporangia, J) side view of sporangia, K) striated spore