Saurauia decolorata Olimpos & Penneys

Olimpos, Shiella Mae B., Penneys, Darin S., Salas, Daryl S., Coritico, Fulgent P., Amoroso, Victor B. & Fritsch, Peter W., 2024, Saurauia decolorata (Actinidiaceae), a new species from Mindanao, the Philippines, Phytotaxa 658 (1), pp. 99-108 : 101-105

Saurauia decolorata Olimpos & Penneys sp. nov. ( Fig. 2 )

Type:— PHILIPPINES, Mindanao, Province of Bukidnon, Municipality of San Fernando, Barangay Magkalungay, peak of Mt. Malimumu, mossy forest, 1,267 m a.s.l., 7.88388°N, 125.41967°E, 19 Jul 2022, Plants and Lichens of the Southern Philippines Survey 2907 (holotype PNH!, isotypes BRIT!, CAHUP!, CAS!, CMUH!, US!)

Diagnosis: — Saurauia decolorata closely resembles the Philippine species S. avellana Elmer (1908:498) ( Fig. 3 A–C ) in having branchlets and abaxial surface of the leaves that are densely tomentose and scaly, and flowers that are densely clustered, and have white corollas, longitudinal anther dehiscence, and 3–4 styles. Saurauia decolorata can be readily distinguished from S. avellana in having rusty-colored tomentum and scales (vs. reddish brown to yellowish brown), a cordate leaf base (vs. round to slightly obtuse), crenate leaf margins (vs. serrate), 16–21 pairs of secondary veins (vs. 13–17), a shiny and nearly glabrous adaxial leaf surface (vs. dull and sparsely tomentose), a fascicled cymose inflorescence (vs. fascicles of simple or compound umbels) with shorter peduncles (0.5–1.6 vs. 1.6–4.2 cm) and pinkish green outer sepals (vs. light green to yellowish green) that are sparsely scaly (vs. moderately scaly).

Description: —Tree, ca. 6–15 m tall, 10 cm diameter, outer bark light brown, lenticels sparse. Branchlets terete, brown to greenish brown. Distal portions of twigs with dense rusty-colored or orangish brown tomentum and scales; longer scales (1.0– 1.2 mm)appressed to slightly ascending, ovate or ovate-lanceolate, shorter scales (<1 mm)irregularly orbicular to elliptic-ovate. Leaves simple, alternate, chartaceous; petiole 2.5–3.0 cm long, indumentum similar to that of distal twigs; lamina narrowly oblong-elliptic, 19–26 × 6–9 cm, length width ratio 2.9–3.5:1; adaxial surface dark green, shiny, glabrous except for a few ovate or orbicular, rusty-colored scales on lower part of midrib; abaxial surface with dense rusty-colored tomentum and abundant to scattered, appressed to slightly patent, ovate, reddish orange scales on midrib and lateral veins; pairs of secondary veins 16–21, 8–11 mm distant from each other, curved and anastomosing at tips towards leaf margin, impressed and prominent abaxially; tertiary veins reticulate, impressed; base cordate, margin crenate with a red tinge at apex of each tooth and 2–3 mm distance between crenulations, apex obtuse. Inflorescence axillary, fasciculate-cymose (3–6 peduncles per axil), ramiflorous with first- to second-order branching, 2.5–4.0 cm long (peduncle base to distalmost petal apex); flowers 3–5(–9) per peduncle, cup-shaped, 15–19 × 13–17 mm, odorless, ca. 2–3 flowers anthetic at a time; peduncle 0.5–1.6 cm long, brownish green, with dense light green to brown tomentum and sparse, weak, ovate-lanceolate scales (ca. 0.5 mm long or less); bracts 2, subtending pedicel, linear, ca. 2–3 × 1.2–1.4 mm, greenish brown, indumentum similar to that of peduncle, persistent, inconspicuous; pedicel 0.9–1.0 cm long, brownish green, tomentose with scales similar to that of peduncle. Sepals 5, outer sepals 2, orbicular to widely ovate, 5–7 × 5–6 mm, pinkish green (basally green, becoming pinkish green apically), sometimes younger sepals (of buds) reddish green, with sparse, appressed, weak, ovate-lanceolate, green or pink scales; intermediate sepal that partially overlaps inner sepals present, partly scaly resembling outer sepals and partly glabrous similar to inner sepals; inner sepals 2, orbicular to broadly ovate, 5–6 × 6–7.5 mm, white, petaloid, glabrous. Petals 5, fan-shaped, 9.0–11.0 × 4.7–6.0 mm, white, opaque, each overlapping with adjacent petal for 40% of length, erect but apex slightly recurved, unequally retuse on apex and sides, apical sinus 1–2 mm long. Stamens 14–17, in two series, filaments 1–1.4 mm long, glabrous; anthers dorsifixed, longitudinally dehiscent, narrowly oblong, 0.6–0.8 × 0.5–0.7 mm, yellow, anther opening 0.5–0.8 × 0.2–0.4 mm. Ovary globose, 1.4–2.5 × 1.9–2.7 mm, green, glabrous, locules 4, placentation axile, ovules numerous, styles (3–)4, proximal 25% fused, pale greenish white, filiform, 2.9–3.2 mm long, apical portions erect, stigma capitate. Fruits not seen.

Additional specimens examined:— PHILIPPINES. Mindanao: Bukidnon, Municipality of San Fernando, Barangay Namnam, Mount Natampod , tropical lower montane forest, 1,087 m a.s.l., 7.86462°N, 125.42463°E, 22 Jul 2022, Plants and Lichens of the Southern Philippines Survey 2969 (BRIT!, CAHUP!, CAS!, CMUH!, PNH!, US!) ; Misamis Oriental, Gingoog City, Barangay Lunotan, Sitio San Isidro , Mount Balatukan Natural Park , tropical lower montane forest, 1,387 m a.s.l., 8.72982°N, 125.00478°E, 19 Jan 2023, Plants and Lichens of the Southern Philippines Survey 4251 (BRIT!, CAHUP!, CAS!, CMUH!, PNH!, US!) .

Distribution and habitat:— Saurauia decolorata is known from two localities within the Municipality of San Fernando, Bukidnon Province, in the Mt. Pantaron Range. Five individuals were encountered at the summit of Mt. Malimumu, Barangay Namnam at 1,267 m a.s.l. which was a sloped open area with volcanic bedrock. In Mt. Natampod, two individuals of this species were seen at a partially shaded area of the lower montane forest at ca. 1,105 m a.s.l. and growing on loam substrate. In Mt. Balatukan Natural Park, three individuals were observed growing in lower montane forest at 1,387 m a.s.l. on volcanic substrate.

Proposed conservation status: — Saurauia decolorata is only known from 10 individuals total among three localities on Mindanao Island (i.e., seven individuals in Mt. Pantaron Range and three individuals in Mt. Balatukan) with an estimated area of occupancy (AOO) of 12 km 2 ( Bachman et al. 2011). All individuals were observed to inhabit lower montane forest where existing threats such as illegal logging, forest clearing, and over-collection of biological resources (e.g., rattan palm and timber) were observed. If these activities remain unregulated, especially in the case of Mt. Pantaron Range, which is not under legislative protection, the habitats and populations of this new species will be compromised. All these conditions satisfy IUCN criteria B2ab ( IUCN Standards and Petitions Committee 2022) thus, we propose S. decolorata to be listed under the Endangered category.

Etymology:—The specific epithet decolorata refers to the rusty-colored tomentum and scales that densely cover the branchlets and the abaxial leaf surfaces imparting a distinct tarnished appearance to the plant. This feature stands out prominently and serves as the most distinctive characteristic of this taxon.

Discussion:—This taxonomic novelty brings the total number of Philippine Saurauia species to 58, making it the third most species-rich area for Saurauia (after Borneo and Papua New Guinea) in the Malesian phytogeographical region.

Saurauia decolorata also resembles S. elegans ( Choisy 1855: 119) Fernández-Villar (1880:19) ( Fig. 3 D–F ) in sharing, e.g., tomentum color, crenate leaf margins, and shiny, glabrous upper leaf surfaces. However, S. decolorata has broader oblong-elliptic leaves (length/width ratio 2.9–3.5 vs. 3.2–5.9), a cordate leaf base (vs. round) and fewer pairs of secondary veins (16–21 vs. 25–35), a fascicled cymose inflorescence (vs. a panicle), and shorter peduncles (0.5–1.6 cm vs. 6–13 cm). Table 1 lists additional differences among S. avellana , S. decolorata , and S. elegans .

The addition of a new species from Mindanao suggests the urgent need for more taxonomic work in Saurauia , a genus that in the Philippines has never been revised. Species-level identifications in Philippine Saurauia have long been difficult because of the lack of revisionary studies and a clear understanding of species boundaries and morphological variation. Studies like this may revive interest in this genus, and information generated can contribute to narrowing the knowledge gap on its taxonomy and species conservation. Ongoing investigations by the first author on the phylogenetic systematics of Saurauia in the Philippines are expected to result in additional publications on evolutionary relationships, taxonomic revisions, and more new species.

The addition of Saurauia decolorata increases the number of Saurauia species in Mindanao to 28, 13 of which are endemic ( Pelser et al. 2011). Mindanao is known for its extensive mountain ranges, where isolated peaks or “sky islands” function as barriers between the lowlands and neighboring mountains. This geographical setting fosters reproductive isolation of species and formation of unique habitats, making these montane forests into crucibles of evolution with numerous endemic taxa ( Amoroso 2000; Flantua et al. 2020). Moreover, the insular nature of Mindanao further isolates it geographically, thus restricting the exchange of genetic material with neighboring island ecosystems, intensifying the prevalence of unique plant species ( Whittaker & Fernández-Palacios 2007; Kier et al. 2009). For these reasons, most Saurauia species in Mindanao are endemic there and apparently have little chance of dispersing, facts that have important conservation implications.

The Pantaron Mountain Range has still no legislation for its protection despite the number of threatened, endemic, and unique vascular plant species it harbors ( Gronemeyer et al. 2014; Lagunday et al. 2017; Amoroso et al. 2020; Coritico et al. 2022). In addition, the cordillera of Central Mindanao is also experiencing significant forest cover loss due to development, mining, and the unsustainable harvest of biological resources (ESSC 2018; Coritico et al. 2022). If this continues and no conservation programs are initiated, Mindanao will not only lose a biodiversity hub in the Mt. Pantaron Range but also its ancient cultural identity, as the mountains are considered sacred places for the indigenous Manobo, Higaonon, and Bukidnon tribes who continue to coexist with their ancestral forests.

Mt. Balatukan presents a different challenge because it was already declared a protected area (Proclamation no. 1249, s. 2007), but forest clearing and poaching are abundantly evident within the area. Moreover, paramilitary insurgencies, i.e., the New People’s Army, have made parts of it inaccessible, hampering implementation of conservation programs. There is a need for better enforcement of protection laws to ensure that the remaining forest of Mt. Balatukan Natural Park can recover from past disturbance.As scientific data on the protected area’s floristic biodiversity is scarce, botanical surveys should be prioritized to support the enhancement of conservation management. The discovery of Saurauia decolorata will hopefully spark interest in conducting more taxonomic studies and create awareness of the noteworthy, unique, and threatened plants of the protected area.

Figures

FIGURE 2. A–L. Saurauia decolorata. A. Branchlets showing the fascicled inflorescence. B. Branchlets showing the rusty-colored tomentum and ovate to ovate-lanceolate scales and shorter orbicular to elliptic ovate scales. C. Leaf base and abaxial surface. D. Flower E. Fasciculate-cymose inflorescences. F. Calyx G. Ovary and styles H. Longitudinal anther dehiscence and dorsifixed filament insertion. I. Pinkish green outer sepals with sparse lanceolate scales. J. Intermediate sepal exhibiting the outer and inner sepal morph. K. Petaloid inner sepals L. Fan-shaped petals. Photos A and E by Darin Penneys, G by Daryl Salas, and B–J Shiella Mae Olimpos.

FIGURE 3. A–C. Saurauia avellana. A. Branchlets B. Flower C. Abaxial leaf surface covered with yellowish brown tomentum and lanceolate scales. D–F Saurauia elegans D. Branchlets E. Type specimen (H. Cumming 922) showing the paniculate inflorescence F. Branchlets and abaxial leaf surface covered with rusty-colored tomentum and bristle-like scales. Photos A–F by Pieter Pelser (Co’s Digital Flora of the Philippines/PhytoImages) and E from JSTOR Global Plants.