Abstract
Actinostachysminuta Amoroso & Coritico (Schizaeaceae), from Mindanao, Philippines, is described herein as a new species. This species is distinguished from all other species of Actinostachys (grass ferns) by its notably short and narrow fronds, distinct triangular stipe, and bifid apex of the sorophore lamina with profuse white long hairs. This species is distinct from the other known Philippine species of Actinostachys by its diminutive epiphytic habit and a habitat restricted to the trunks of the tree fern Sphaeropterispolypoda (Baker) R.M.Tryon. A taxonomic key to the species of Philippine Schizaeaceae that incorporates the new species is provided.
Keywords: ferns, lowland tropical rainforest, Mount Hamiguitan Range Wildlife Sanctuary, Schizaeaceae
Introduction
The fern family Schizaeaceae comprises two genera, Actinostachys and Schizaea, and ca. 30‒35 species widely distributed in tropical and south-temperate regions (PPG I 2016; Smith et al. 2006; Chen et al. 2017). In the Philippines, the family is represented by two species of Schizaea: S.dichotoma (L.) Sm. and S.malaccana Bak., and two species of Actinostachys: Actinostachysdigitata (L.) Wall. and A. inopinata (Selling) C.F.Reed (Barcelona et al. 1996). Of these, S.dichotoma and S.malaccana are distinctive by having the sorophores attached pinnately to an elongate axis. Schizaeadichotoma is easily recognized by the dichotomously branching sterile portions of the frond, whereas S.malaccana has an unbranched sterile portion. The two species of Actinostachys, A.digitata and A.inopinata, both have digitately arranged sorophores and are differentiated by the relative width of their lamina and by the number of sporangial rows (4-seriate or biseriate, respectively) (Holttum 1955; Barcelona et al. 1996). Moreover, the different species of Schizaea and Actinostachys are classified into sub-genera and sections based on the exospore (smooth or striated to pitted) and spore size (Reed 1947).
All four Philippine species of the family Schizaeaceae are reported in Mount Hamiguitan Range Wildlife Sanctuary (MHRWS), a protected UNESCO World Heritage Site (Amoroso et al. 2016; Amoroso et al. 2018). During fieldwork in MHRWS in 2016 and 2018, we encountered unusual individuals of Actinostachys growing on the trunks of tree ferns. On careful examination of these plants, available type images from JSTOR Global Plants, and in consultation of the literature, we conclude that they represent a species new to science. Here we describe this new species and provide detailed photographs of it along with a key to the five Philippine species of Schizaeaceae, all of which are found in MHRWS.
Taxonomy
Actinostachys minuta
Amoroso & Coritico sp. nov.
5B8ADE52-E2E8-5904-A5FF-15D8D33393AC
urn:lsid:ipni.org:names:77209910-1
Figure 1.
A the tree fern Sphaeropterispolypoda with associated vegetation. The trunks of this tree fern species serve as the substrate of ActinostachysminutaB close-up view of in-situ epiphytic habitat of A.minuta embedded in the trunk of S.polypoda with the moss Leucobryum sp.
Figure 2.
ActinostachysminutaA habit with distinct stipe (st), unbranched fronds with 3 sorophores (so) attached at the tip of lamina (la), (inset) elongate rhizome (rh), with persistent gametophyte (ga) and uniseriate hairs B transection of the stipe showing flattened xylem (x) C lamina with distinct costa (co) D single row of stomata (sm) on each side of costa E elongated rhizome with long uniseriate hairs (uh) F digitate sorophores attached at the tip of the sterile lamina G bifid apical lamina of sorophore H portion of sorophore with reflexed lamina margins and biseriate sporangia, I. Monolete spore.
Diagnosis.
This new species Actinostachysminuta is most similar to Actinostachysplana (Fourn.) Reed but differs by its shorter and narrow fronds with a distinct triangular stipe, sorophore lamina longer and narrower with white long hairs and sorophores 1‒4 but usually 1. It differs from the other four Philippine species by its restricted epiphytic habit on the trunk of the tree fern Sphaeropterispolypoda (Baker) R.M. Tryon.
Type.
Philippines • Mindanao Island. Davao Oriental: San Isidro Municipality, Mount Hamiguitan Range Wildlife Sanctuary, 622 m a.s.l., 10 October 2016, V.B. Amoroso 11213 with F.P. Coritico (holotype: PNH; isotypes: BRIT, CMUH).
Description.
Epiphytic on trunks of the tree fern Sphaeropterispolypoda with rhizome embedded between adventitious roots. Rhizome: short-creeping to erect, black, becoming elongate, attached to the persistent tuberous gametophyte with profuse, long, uniseriate, pale brown hairs. Fronds: crowded, pendulous, grass-like, unbranched, up to 3.0–4.5 cm long; stipe distinct, black, oblong to triangular in transection, 5–8 mm long, with short scattered glandular hairs, with a few large cortical sclerenchymatous cells, vascular tissues reduced with single flattened xylem strand; lamina (sterile portion) simple, unbranched, flattened, up to 2.5–3.7 cm × 0.8‒1.0 mm wide, margin entire, adaxial surface with distinct costa and scattered uniseriate hairs, the basal cells of the hairs persistent and forming scattered warts and disappearing distally; stomata arranged in one row (uniseriate) on each side of costa; sorophores 1 to 4 per frond but mostly 1, sessile or attached by a short stalk at apex of lamina, digitately arranged, 4–6 mm long; laminae of sorophores covered with profuse white long hairs adaxially, margin entire, apex bifid; sporangia in 2 rows, nearly symmetrically arranged, completely covering abaxial surface and protected by reflexed edge of sorophore lamina, sessile, ellipsoidal, with distal annulus, surface striated, glabrous; spores monolete, smooth.
Distribution and habitat.
This species is currently known only within the buffer zone located outside the boundaries of MHRWS in San Isidro Municipality, in shaded habitat in lowland tropical rainforest at 622 m a.s.l. It grows strictly as an epiphyte on trunks of the tree fern Sphaeropterispolypoda with rhizomes embedded between adventitious roots in association with the moss genus Leucobryum and has not been observed terrestrially. The vegetation surrounding Sphaeropterispolypoda with Actinostachysminuta consists of trees 20–30 meters tall, including Canariumasperum Benth., Dilleniaphilippinensis Rolfe, Gymnostomarumphianum (Miq.) L.A.S.Johnson, Lithocarpus spp., Pittosporumeuphlebium Merr., and Shoreapolysperma Merr., and tree ferns such as Alsophilalurida (Blume) Hook. and Sphaeropteriselmeri R.M.Tryon. The ground cover is dominated by other fern and lycophyte species such as Dicranopterislinearis (Burm. f.) Underw., Lindsaeagueriniana (Gaudich.) Desv., Nephrolepisbiserrata (Sw.) Schott, Schizaeadichotoma, Selaginellajagori Warb., Selligueataeniata Parris, and Taenitisblechnoides (Willd.) Sw., as well as several species of Calamus.
Additional specimens examined.
Philippines, Mindanao, Davao Oriental Province, Municipality of San Isidro, Mt. Hamiguitan Range Wildlife Sanctuary, 06°44'15.24"N, 126°08'59.36"E, 622 m a.s.l., 16 June 2018, V.B. Amoroso 13515 with F.P. Coritico (CMUH).
Etymology.
The specific epithet refers to the diminutive size of the fronds relative to the other species in the genus.
Suggested common name.
Diminutive grass fern.
Notes.
The traditional treatment of Schizaeaceae includes all species with digitately (connate) and pinnately arranged sorophores in Schizaea as in Barcelona et al. (1996), Barcelona (2011), Holttum (1955) and Kramer (1990). Here we follow the classification of PPG 1 (2016) segregating them into two genera Schizaea (species with pinnately arranged sorophores) and Actinostachys (species with digitately arranged sorophores) and by less easily observed features of their gametophytes (tuberous in Actinostachys versus filamentous in Schizaea) (Bierhorst 1968, 1971) and based on phylogenetic evidence (Labiak and Karol 2017; Wikstrom et al. 2002). The size of the fronds and sorophores is used in identifying the species of the family Schizaeaceae (Barcelona et al. 1996). However, the length of the sorophore is a much more reliable character than the length of the whole frond because the short sorophore is much less influenced by environmental conditions than the whole frond (Brownsey and Smith-Dodsworth 2000). In this respect, the new species and the closest related species (A.plana) differ from all other species of Actinostachys in its very short sorophores, about 2.5–6 mm long.
We compare the new species to three other digitate species of Actinostachys that are most similar to it in morphology based on the published descriptions of Bierhorst (1968), Holttum (1955), Barcelona et al. (1996), Reed (1947) and Sofiyanti et al. (2019), as well as examinations of JSTOR type images viz., A.plana, A.spirophylla, and A.wagneri. Our new species is closest morphologically to A.plana, followed by A.spirophylla Troll, and A.wagneri Sell. (Table 1). Actinostachysminuta shares an epiphytic habitat with A.plana, A.spirophylla and A.wagneri, growing in moss cushions on tree fern trunks, although Holttum (1955) did not explicitly mention tree fern trunks but simply trees.
Table 1.
Major characters delineating Actinostachysminuta from A.wagneri, A.spirophylla and A.plana
| Character | A.wagneri (Holttum 1955; Reed 1947) | A.spirophylla (Holttum 1955; Reed 1947) | A.plana (Reed 1947) | A.minuta |
| Habitat | Epiphytic on stumps and bases of trees | Epiphytic in moss-cushions on trees | Epiphytic on tree ferns | Strictly epiphytic on trunks of the tree fern Sphaeropterispolypoda |
| Stipe | Indistinct | Indistinct | Distinct (5.5–7.5 long mm) flat | Distinct (5–8 mm long) triangular in transection |
| Lamina (sterile portion) length (cm) | 6–20 | 4–8 | 5.5–10.2 | 2.5–3.7 |
| Lamina (sterile portion) width (mm) | 0.5–0.7 | Ca. 1.5 | 1.4–1.74 | 0.8–1.0 |
| Number of stomatal rows on each side of costa | 1 | 1 | Not described | 1 |
| Sorophore length (mm) | 7–15 | 4–8 | 2.5–4.8 | 4–6 |
| Sorophore number | 2 to 5 | 1 to 3 | 3 to 6 but usually 4 | 1 to 4 but usually 1 |
| Sorophore lamina apex | Not bifid, glabrous | Not described | Bifid or toothed | Bifid with profuse white long hairs |
| Sorophore lamina width (mm) | Not described | Not described | 0.5–0.8 | 0.5–0.6 wide |
| Sporangia | Biseriate with brown hairs | Biseriate (sometimes apparently tetraseriate) and glabrous | Biseriate | Biseriate and glabrous |
| Spore surface | Striate | Striate | Smooth | Smooth |
| Distribution | Northeastern Australia, Indonesia (Borneo, Moluccas), Malaysia (Peninsular Malaysia), Papua New Guinea, Singapore, Thailand | Indonesia (Moluccas), Malaysia (Peninsular Malaysia), Micronesia (Ponape) | New Caledonia (Sommet du Mont Mi) | Philippines (Mindanao) |
The sorophores of A.plana and A.spirophylla come closest in length to those of A.minuta (2.8–8 mm long versus 4–6 mm). In addition to the shorter sorophores, however, our new species is distinguished from A.plana by several other features, viz., shorter (2.5–3.7 cm long) and narrower (0.8–1.0 mm) lamina (sterile portion) with distinct triangular stipe up to 8 mm long (versus longer and wider (5.5–10.2 cm × 1.4–1.74 mm) and with flattened stipe in A.plana) and longer and narrower sorophores (4–6 × 0.5–0.6 mm vs. 2.5–4.8 × 0.5–0.8 mm).
It is interesting to mention that we found a persistent gametophyte in our new species as also reported by Bierhorst (1968) in Actinostachysoligostachys Bierh., A.melanesica C.F.Reed, A.intermedia (Mett.) C.F.Reed, and A.laevigata (Mett.) C.F.Reed. The tuberous gametophyte is attached to the well-developed sporophyte (Fig. 2A).
All five species of Philippine Schizaeaceae are found in MHRWS in shaded forest. Except for A.minuta which is epiphytic on the trunks of tree ferns, the other four species are terrestrial, inhabiting an ultramafic soil with fallen leaves of Gymnostomarumphianum.
Conservation status.
Although MHRWS is a protected area, we only have observed this species from the type locality. The species occurs within the buffer zone of San Isidro, MHRWS with an estimated number of 30 individuals growing strictly on trunks of tree ferns. Its location in the buffer zone and the over-collection of tree fern trunks as a medium to grow other plants and for the making of handicrafts will likely reduce the populations of the species if this threat continues. Thus, we recommend listing the species as Critically Endangered (CR) based on its very small and restricted population with ≤ 50 mature individuals and the extent of occurrence estimated to be < 10 km2 (IUCN Standards and Petition Committee 2019).
Key to the genera and species of grass ferns (Schizaeaceae) from the Philippines
| 1a | Sorophores attached pinnately arranged or comb-like | Schizaea |
| 2a | Fronds repeatedly dichotomously branched; lamina ≥ 2 mm wide | S.dichotoma |
| 2b | Fronds unbranched; lamina < 2 mm wide | S.malaccana |
| 1b | Sorophores digitate | Actinostachys |
| 3a | Lamina ≥ 2 mm wide; sorophores 1.0‒5.0 cm long | 4 |
| 4a | Lamina (sterile portion) ≤ 5 mm wide; stomata in one row on each side of costa; sporangia in four rows on the sorophores | A.digitata |
| 4b | 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 |
| 3b | Lamina < 2 mm wide; sorophores < 1.0 cm long | A.minuta |
Supplementary Material
Acknowledgements
This research was supported by the Department of Science and Technology-Grant-in-Aid (DOST–GIA) and the U.S. National Science Foundation (DEB-1754697). We thank the Department of Environment and Natural Resources – Region 11 for the issuance of Gratuitous Permit XI-2019-21, Office of the Park Superintendent of Mt. Hamiguitan Range Wildlife Sanctuary, and the administration of Central Mindanao University led by Dr. Jesus Antonio G. Derije for logistical support, and the Department of Science and Technology – Philippine Council for Agriculture, Aquatic and Natural Resources Research and Development (DOST-PCAARRD) for monitoring the research. This manuscript was improved by the valuable comments of two anonymous reviewers.
Citation
Amoroso VB, Coritico FP, Fritsch PW (2020) Actinostachys minuta, a new species of grass fern from Mindanao, Philippines. PhytoKeys 151: 59–66. https://doi.org/10.3897/phytokeys.151.53100
References
- Amoroso VB, Coritico FP, Fritsch PW. (2016) Species richness and conservation status of ferns and lycophytes in Mt. Hamiguitan Range Wildlife Sanctuary, Davao Oriental, Philippines. Philippine Journal of Science 145(2): 127–137. [Google Scholar]
- Amoroso VB, Acma FM, Coritico FP, Gorme FS, Lagunday NE, Salolog MCS, Colong RD. (2018) Floral diversity assessment of the buffer zones and vicinity of the Mt. Hamiguitan Range Wildlife Sanctuary (MHRWS), Davao Oriental: Basis for inclusion to protected area zone. Philippine Journal of Systematic Biology 12(2): 36–51. [Google Scholar]
- Barcelona J. (2011) Pteridophytes (Lycophytes and Monilophytes). In: Pelser PB, Barcelona JF, Nickrent DL (Eds) Co’s Digital Flora of the Philippines. www.philippineplants.org
- Barcelona JF, Hernaez B, Price MG. (1996) Philippine Schizaea. Asia Life Sciences 5(1): 27–34. [Google Scholar]
- Bierhorst DW. (1968) Observations on Schizaea and Actinostachys spp., including A.oligostachys sp. nov. American Journal of Botany 55(1): 87–108. 10.1002/j.1537-2197.1968.tb06949.x [DOI] [Google Scholar]
- Bierhorst DW. (1971) Morphology of Vascular Plants. Macmillan, New York.
- Brownsey PJ, Smith-Dodsworth JC. (2000) New Zealand Ferns and Allied Plants. David Bateman Ltd., Auckland City, 168 pp. [Google Scholar]
- Chen CW, Perrie L, Glenny D, Chiou WL. (2017) SOL Amazing Lycophytes and Ferns of the Solomon Islands. National Museum of Natural Science, Taichung City, 550 pp. [Google Scholar]
- Holttum RE. (1955) A Revised Flora of Malaya (edition 1, vol. 2). Ferns of Malaya: 52. Government Printing Office, Singapore, 653 pp. [Google Scholar]
- Kramer KU. (1990) Schizaeaceae. In: Kramer KU,Green PS (Eds) The Families and Genera of Vascular Plants, vol. 1, Pteridophytes and Gymnosperms. Springer Verlag, New York, 258‒263. 10.1007/978-3-662-02604-5_44 [DOI]
- Labiak PH, Karol KG. (2017) Plastome sequences of an ancient fern lineage reveal remarkable changes in gene content and architecture. American Journal of Botany 104(7): 1008–1018. 10.3732/ajb.1700135 [DOI] [PubMed] [Google Scholar]
- PPG I (2016) A community-derived classification for extant lycophytes and ferns. Journal of Systematics and Evolution 54(6): 563–603. 10.1111/jse.12229 [DOI] [Google Scholar]
- Reed CF. (1947) The phylogeny and ontogeny of the Pteropsida. Schizaeales. Boletim da Sociedade Broteriana 2(21): 71–197. [Google Scholar]
- Smith AR, Pryer KM, Schuettpelz E, Korall P, Schneider H, Wolf PG. (2006) A classification for extant ferns. Taxon 55(3): 705–731. 10.2307/25065646 [DOI] [Google Scholar]
- Sofiyanti N, Iriani D, Fitmawati DI. (2019) The first record of grass-like fern, Schizaeadichotoma (L.) J. Sm. (Schizaeaceae) from Lingga Island, Indonesia: Its morphological, anatomical and palynological study. Biodiversitas (Surakarta) 20(9): 2651–2660. 10.13057/biodiv/d200930 [DOI] [Google Scholar]
- Standards IUCN, Petitions Committee (2019) Guidelines for Using the IUCN Red List Categories and Criteria. Version 14. http://www.iucnredlist.org/documents/RedListGuidelines.pdf
- Wikstrom N, Kenrick P, Vogel JC. (2002) Schizaeaceae: A phylogenetic approach. Review of Palaeobotany and Palynology 119(1–2): 35–50. 10.1016/S0034-6667(01)00128-2 [DOI] [Google Scholar]
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