Schizaea erecta Amoroso & Coritico, 2023

Amoroso, Victor B., Acola, Mescel S., Guiang, Maria Melanie M., Acma, Florfe M., Fritsch, Peter W. & Coritico, Fulgent P., 2023, A new species of grass fern, Schizaea erecta (Schizaeaceae), from Dinagat Island, Mindanao, Philippines, Phytotaxa 618 (3), pp. 265-273 : 267-272

Schizaea erecta Amoroso & Coritico , sp. nov ( Figs. 2–4 )

Type:— PHILIPPINES. Dinagat Island: Municipality of Tubajon , Paragua Forest , 10.29355°N, 125.58594°E, 65 m, 30 January 2023, V. B . Amoroso with F. P . Coritico & M. M . Guiang. 3003 (holotype PNH!, isotypes CMUH!, BRIT!) .

Diagnosis: — Schizaea erecta resembles S. dichotoma in having hairy rhizomes, dimorphic fronds, stipes with a t-shaped xylem strand, laminae fan-shaped and branching dichotomously, stomata hypocytic, sorophores pinnately arranged in 2 rows, and sporangia with long non-glandular hairs, but differs by having a rhizome with short-appressed brown hairs (vs. long, coarse brown hairs), the stipe longer and up to 26.6 cm long with a narrow groove (vs. up to 20 cm long and deeply grooved), fronds 3–5 times branching dichotomously (vs. 6–8 times branching), narrower (8–14 cm long by 2.0– 4.5 cm wide), and consistently erect fronds (vs. 15 cm long by 17 cm wide, not erect), sorophores up to 39 per stipe with 12–16 lobes alternately arranged (vs. up to 34 with 5–10 lobes oppositely arranged), and sporangia oblong with long white hairs (vs. reniform with brown hairs).

Description:—Terrestrial, 30–50 cm long. Rhizomes short creeping, 1.5–5.0 cm below ground, 0.3 mm thick, covered with persistent shiny brown appressed hairs 1–2 mm long. Fronds dimorphic, crowded, irregularly branched; sterile fronds: erect, stipes distinct, 18.5–26.6 cm long, base partly buried in ground, blackish and becoming light green in upper portion, slightly winged at middle to distinctly winged at apex, with shallow groove and scattered short hairs; laminae fan-shaped, 9–15 cm long and each axis 1 mm wide, whole laminae 2–4 cm wide, costae distinct, branching dichotomously 3–5 times; fertile fronds erect, stipes 11–27 cm long, tetragonal in transection and distinctly winged in upper portion; lamina fan-shaped, 8–14 × 2.0– 4.5 cm, branching dichotomously 3–5 times, basal branch slightly flattened, 1–2 mm wide, distal branch up to 0.5 mm wide with scattered small projections (bases of glandular hairs). Sorophores born distally of each branch of frond, 5–12 mm long, 24–39 per stipe, bearing 12–16 pairs of lobes, pinnately arranged in 2 rows and opposite in arrangement. Sporangia in two rows associated with long white non-glandular hairs, with opposite to alternate arrangement, loosely arranged at base and tightly packed in upper part, oblong with short stout stalk, brown, annulus apical, opening by a vertical slit. Spores monolete and reniform, 37 µm in diameter.

Etymology:—The specific epithet refers to the erect fronds of the species.

Suggested common name:— Dinagat grass fern.

Distribution and habitat: — Schizaea erecta is known only from open habitat at 65 m elevation. It grows as a terrestrial plant in colonies with rhizomes growing below the ground in ultramafic soil associated with plants such as Dicranopteris linearis ( Burman 1768: 235) Underwood (1907: 250) , Imperata cylindrica ( Linnaeus 1759: 878) Palisot de Beauvois (1812: 165) , Piper sp. , Pteridium aquilinum ( Linnaeus 1753: 1075) Kuhn in Decken (1879: 11), Pteris cretica Linnaeus (1767: 130) , and Smilax sp. ( Figure 5 ).

Conservation Status:— Dinagat Island was identified as a critical terrestrial conservation priority in the Philippines ( Ong et al., 2002). Logging, mining, and land conversion threaten the entire island ( Haribon, 2004). Schizaea erecta is known only within the Paragua forest, Municipality of Tubajon, with an estimated number of 30 individuals growing in just one open area near agricultural land. The habitat is prone to land conversion because of nearby residential areas. Thus, we recommend listing the species as critically endangered based on its restricted population with ≤ 50 mature individuals and the extent of occurrence estimated to be ≤ 10 km 2 (IUCN Standards and Petition Committee 2019).

Discussion: — Schizaea erecta is most similar to S. dichotoma , based upon descriptions of Holttum (1959) and Sofiyanti et al. (2019), and examination of JSTOR type images and Co’s Digital Flora of the Philippines ( Table 1 ). The species share nearly the same height and the presence of hairs on their rhizomes. Their fronds are dimorphic with fan-shaped lamina which branch dichotomously, they both have hypocytic stomata, and they both possess two rows of sorophores. However, the new species differs from S. dichotoma in having rhizome hairs 1.0– 2.3 mm long (vs. 2–3 mm) ( Figure 2B ); sterile fronds branching dichotomously 4–5 times (vs. 6–8 times) ( Figure 2C ). Further, the frond is consistently erect whereas that of S. dichotoma is not erect ( Figure 2A ). The sorophore of S. erecta has 12–16 pairs of lobes whereas S. dichotoma has 5–10 pairs. The sporangia of S. erecta are oblong whereas S. dichotoma has reniform sporangia ( Figure 2G, H ).

Ke et al. (2022) and Brownsey & Perrie (2014) stated that the S. dichotoma complex exhibits wide morphological and cytological variation. However, most members of this complex are poorly characterized and have been collectively lumped into “ S. dichotoma ”, which was found to be polyphyletic in the phylogeny of Ke et al. (2022). Although our new species was not included in this phylogeny, we reckon that it is morphologically so distinct that it merits treatment as a separate species, especially in anticipation of further splitting in this group. With the recognition of this new species, there are now 21 species of Schizaea worldwide (PPG I, 2016) and three in the Philippines.

The salient anatomical features of Schizaea erecta include the following: the rhizome is almost circular with appressed hairs as outgrowths of the epidermal cells. The cortex is mainly composed of parenchyma cells. The stele is a haplostele with the phloem surrounding the xylem tissue ( Figure 3B ). The stipe shape changes from tetragonous at the base with indistinct costa and concave with narrow groove at the middle and somewhat flattened in the upper stipe with two distinct grooves and wings. The cortex becomes complex, being composed of the outer cortical sclerenchyma and the inner cortical parenchyma cells with the stele becoming actinostele and with a T-shaped xylem strand ( Figure 3C–E ). The lamina is flattened at the lower axis with distinct costa and incurved at the apical axis. The outer wall of the smaller epidermal cells is thickened and inwardly with large hypodermal cells. The vascular bundle is surrounded by a layer of large endodermis and a single layer of pericycle as also reported by Sofiyanti et al. (2019). Moreover, both surfaces of the costa have large sclerenchyma cells to protect the inner undifferentiated mesophyll from drying as the plants are found in open area. The guard cells protrude on the abaxial surface of the epidermis and connect to the large intercellular spaces.

The anatomy of Schizaea erecta differs from that of S. dichotoma in the rhizomes for having larger outer cortical cells and smaller inner cortical cells (vs. smaller outer cortical cells and larger inner cortical cells), vascular bundles surrounded by ring-like sclerenchymatous cell layers (vs. star-shaped sclerenchymatous cell layers), numerous metaxylem (vs. 4 metaxylem); stipe tetragonous at the base and flattened in the upper stipe with narrow groove (vs. M-shaped and deeply grooved); lamina narrowly grooved (vs. deeply grooved), and guard cells protruding from the abaxial surface (vs. guard cells sunken).

Figures

FIGURE 2. Schizaea erecta. A. Habit showing erect axis. B. Short-creeping rhizome. C. Dichotomous branching of lamina. D. Distal branch showing scattered projections of glandular hairs. E. Bases of glandular hairs. F. Sorophore. G. Lobes of sorophore showing the 2 rows of oblong sporangia with long white non-glandular hairs, and spore (inset). H. Dehisced sporangia showing vertical slit and long, white, non-glandular hairs.

FIGURE 3. Schizaea erecta. Habit (A) and anatomy (B–J): A. Habit. B. Rhizome (c—cortex). C. Basal Stipe (ocs—outer cortical sclerenchyma, ics—inner cortical slerenchyma, x—xylem, ph—phloem). D. Middle stipe (g—groove). E. Apical stipe (w—wing). F. Lamina (1st branch) (c—costa). G. Lamina (2nd branch) (m—mesophyll, e—epidermis, h—hypodermis, x—xylem, ph—phloem). H. Lamina (3rd branch). I. Lamina (4th branch) (gc—guard cells, is—intercellular spaces). J. Lamina (5th branch).

FIGURE 4. Schizaea erecta. A. Single row of stomata on each side the of costa. B. Hypocytic stomata (c—costa; st—stomata).

FIGURE 5. Habit and habitat of Schizaea erecta.