Pinanga gruezoi Adorador & Fernando, 2020

Adorador, Jiro T., Meneses, Zhereeleen D. & Fernando, Edwino S., 2020, Pinanga gruezoi (Arecaceae), a new slender clustering palm from the Philippines with notes on an amended description of P. samarana, Phytotaxa 429 (2), pp. 120-134 : 121-128

Pinanga gruezoi Adorador & Fernando , sp. nov.

Type:— PHILIPPINES, Samar Province: Samar Island, San Jose de Buan , Mt. Huraw , 850 m elev, 16 July 2015, Adorador 004 (holotype LBC!; isotypes CAHUP!, PNH!, K!)

Diagnosis: — Pinanga gruezoi is similar to P. heterophylla and P. modesta ., The new species is different from the former in its smaller middle leaflet dimension (up to 26 × 4.5 cm), distichous floral cluster arrangement along rachillae, and broader (up to 9 mm) ovoid–ellipsoid fruits; while it deviates from the latter in its coriaceous leaflets which are abaxially glabrous and inflorescence with more numerous (4‒9) yet shorter (up to 9 cm) arching to reflexed rachillae that bear closely-set (up to 5 mm apart) fruits.

Clustering, slender undergrowth palm, to 3m tall. Stem to 0.8‒1.5 cm diam., internodes 1.8‒4 cm apart. Crownshaft elongate c. 20 cm long, cylindrical, slightly swollen. Leaves up to 6 in crown, axes reddish when young, sheath 10.5‒20 × 1‒2 cm, yellowish green with sparse brown scaly indumentum, slightly glaucous, ligules (extension of leaf sheath) 1‒2 cm long, narrowly triangular, leaf without sheath but including petiole 65‒80 cm long, petiole (6‒)14‒35 × 0.5 cm, shallowly channelled adaxially, convex abaxially sparsely covered with brown indumentum, rachis angular, (23‒)35‒50 × 0.3 cm, bifacial adaxially and rounded abaxially with brown scaly indumentums similar to that of the petiole. Leaflets 5‒11 per side of the rachis, coriaceous, ± sigmoidal, generally multicostulate except occasionally for basal leaflets, ± regularly arranged, 2‒7 cm apart, the apex long acuminate to subfalcate, glossy green adaxially drying grayish (when preserved in alcohol), much paler green abaxially drying brownish, with midfixed filamentous ramenta along the midrib to 3 mm long; basal leaflets 1‒7-costulate, 13‒27 × 2‒4 cm, middle leaflets 2‒6-costulate, 14.5‒26 × 1.3‒4.5, apical leaflets 5‒11-costulate, 10.5‒18 × 2.3‒6 cm, joined basally up to 11 cm along the rachis. Inflorescence 5‒12 cm long, prophyll unknown, peduncle 1‒2.2 × 0.3‒0.6 cm, rachis 1.7‒6 cm long, rachillae bracts gibbous, 1 mm high, rachillae 4‒9 reflexed, (2‒) 6‒9 cm long, subdistichous to spirally arranged along rachis; flowers distichously arranged. Staminate flowers c. 6 × 2.5 mm, calyx 1 mm high, 3-lobed, joined at the base, petals valvate, 5 × 2 mm, narrowly oblique triangular, stamens 9, filaments 0.5 mm long, anther basifixed, 1 mm long. Pistillate flowers 1 × 2 mm, with broadly ovate imbricate calyx and corolla lobes. Fruit ovoid‒ellipsoid to fusiform, 1.4‒1.8 × 0.7‒0.9 cm, distichously arranged, ripening red to purplish black, fruits inserted to 5 mm apart, 7‒12 fruits per side of rachillae, fruiting perianth 2 × 3 mm, not contracted at the mouth. Seed ovoid‒ellipsoid, 1 × 0.7 cm, rounded apically, shallowly concave below. Eophyll bifid, 4‒costulate. ( Figures 1 & 2 ).

Distribution and Habitat: — Pinanga gruezoi is found on the islands of Samar, Dinagat, Bucas Grande, and northeastern Mindanao ( Figure 3 ). The new species is widespread across many forest types at differing elevation range (20‒856 m elev.), viz. lowland evergreen forest, forest on limestone, and forest on ultramafic soil. Typically it is abundant thriving on light-exposed areas in the forests such as slopes and ridges.

Local Name:— The local field guides referred to this palm as tagibungang–liitan (tagibunga refers to P. samarana , and liitan = small) to account for its diminutive habit. Thus, to avoid nomenclatural confusion, this paper formalizes Gruezo gasigan as the official common name for this new species. The common name gasigan refers to P. heterophylla to which it closely resembles.

Specimens examined:— PHILIPPINES. Samar Island: Samar Province, San Jose de Buan, Mt. Huraw , 856 m elev., 16 July 2015, J. T. Adorador 004 (holotype LBC! Isotype CAHUP, LBC, EBL, K) ; Hinabangan, Barangay Consolabao, Sitio Arizona , c. 280 m elev., 12 July 2015, J. T. Adorador 008 ( LBC! PNH! K!), J. T. Adorador 009 ( LBC! PNH!), 11 February 2016, J. T. Adorador 024 ( LBC! CAHUP!), 12 February 2016 J. T. Adorador 080 ( LBC! PNH!) ; Paranas, Brgy. Tenani , 388 m elev., 12 February 2016, J. T. Adorador 053 ( LBC! PNH!), J. T. Adorador 061 ( LBC! EBL). Eastern Samar Province, General MacArthur, Barangay Vigan, c. 208 m elev., 26 February 2016, J. T. Adorador 092 ( LBC! PNH!) ; Llorente, Mt.Apoy, 240 m elev., May–June 1969, H. G. Gutierrez et al. 467 ( PNH!). Dinagat Island : Dinagat Province, Libjo , Paragua forest , 216 m elev., 2016, E. P. Lillo LDLP2 SP57 ( LBC!), 208 m elev., LDLP3 SP8 ( LBC!), Loreto, lower slopes of Mt. Redondo , 648 m elev., 01 September 2016, E. S. Fernando 4164 ( LBC!). Bucas Grande Island : Surigao del Norte Province, June 1919, Ramos & Pascasio BS 359098 ( P! [ P02147347 ]). Mindanao Island : Surigao del Norte Province, Claver, Barangay Taganito, 45 m elev., 02 July 2010, E. S. Fernando 2263 ( LBC!, PNH!), 45 m elev., 02 April 2011, E. S. Fernando 2375 ( LBC!, PNH!) .

Conservation status:— The area of occupancy (AOO) of Pinanga gruezoi is calculated at 32 km 2 thus we regard this species as Endangered [EN B2 b(ii, iii, v) c(iv)]. P. gruezoi has been documented in eight unique locations across four islands (Samar, Dinagat, Bucas Grande, and northeastern Mindanao). Limited palm surveys in Samar Island Natural Park (SINP) last February 2016 across different forest types (within twelve 20 m × 20 m nested plots) in five sites altogether recorded 310 palm individuals (92 mature, 150 saplings, and 68 seedlings) ( Adorador 2016 unpublished data). Across the currently known locations of this species, a continuing decline is projected in its area of occupancy, extent and/or quality of habitat, and number of mature individuals. Furthermore, qualitative assessment of the habitat showed extreme fluctuations in its number of mature individuals since extirpation was observed in its local subpopulations on Samar Island due to slash-burn farming and illegal logging; and in northeastern Mindanao due to mining activities.

Etymology:— This slender palm is named after Dr William Sm. Gruezo, a retired Professor of Plant Biology Division, Institute of Biological Sciences, College of Arts and Sciences, University of the Philippines Los Baños. This species is dedicated in acknowledgement of Dr Gruezo’s contribution to systematics and conservation of Philippine plants.

Notes:— The morphological differences of Pinanga gruezoi from other Philippine congeners is hypothesized to be indicative of reproductive isolation due to the physical geographic boundaries (see Figure 3 ). Considering the palm’s documented morphological variability across the different forest types and elevation gradients, and the absence of major barriers across its geographic occurrence, these forms constitute just a single broadly circumscribed species under the biological species concept ( Mayr 2000).

The new species belongs to a subset of Philippine Pinanga characterized by their slender stems (typically up to 2 cm diam.), leaves with few (less than 11) falcate-sigmoid pluricostulate (2‒8-costulate) leaflets, and rather few rachillae (1‒9)—which is herein referred as the Modesta group ( Table 1). This functional group includes two solitary-stemmed taxa, P. egregia Fernando (1994: 775) and P. isabelensis Beccari (1919a:318) , and a subgroup of clustering species that includes P. gruezoi , P. heterophylla Beccari (1919a: 319) , P. modesta Beccari (1907: 225) and P. geonomiformis Beccari (1909: 602) . P. gruezoi is unique among the subset with caespitose stems by a combination of the following characters: typically more coriaceous leaflets (5‒11 per side of rachis) which are glabrous underneath, inflorescence with relatively more rachillae (4–9) but are rather short ((2‒) 6‒9 cm) and arching to reflexed, which bear relatively large (up to 1.8 × 0.9 cm) distichously arranged and closely-set (just 5 mm apart) ovoid-ellipsoidal fruits. Among the other members of the group, P. heterophylla is the most similar to P. gruezoi but the former has much larger middle leaflet dimension, 3-seriate flowers clusters along the rachillae and narrowly ovoid-ellipsoid fruits. Meanwhile, P. modesta is decidedly different from the new species due to its subpapyraceous leaflets which are abaxially subglaucescent, fewer and longer more rigid-straight rachillae and ovoid fruits with conical-acuminate apex that are widely spaced along rachillae. Additionally, P. gruezoi superficially resembles P. geonomiformis but the latter has fewer leaflets per side of rachis which are thinly papyraceous and an inflorescence which bears only one rachilla.

The above-mentioned shared features of the Modesta group can be used to easily distinguish P. gruezoi from the other known clustering Pinanga in the Philippinensis group, namely P. sobolifera Fernando (1994: 49) and P. philippinensis Beccari (1889: 180) . These two species contain more (10‒40) ±linear-lanceolate (typically 1 ‒ 2-costulate) leaflets per side of the rachis and more number of rachillae (8‒20). P. sobolifera deviates further from the new species in its stoloniferous habit and spirally arranged floral clusters along the rachillae. On the other hand, P. philippinensis should not be confused with P. gruezoi since the former has conspicuously thicker stem, fibrous leaf sheath margins, and longer rachillae which bear more fruits per side.

As observed on Samar Island, this novel taxon could be found across the three forest formations which could account for their morphological variations. Those populations found on lowland up to lower montane forests and over ultramafic rocks are characterized by 2‒5-costulate leaflets ( Figure 1 A–B & D–E ) and more number of rachillae (5–8) ( Figure 1 G–H ). Meanwhile, populations found over limestone typically have 2-costulate leaflets ( Figure 1 F ) and few rachillae ( Figure 1 I ). Moreover, those on lowland and lower montane forests exhibit accentuated reddish to maroon colourations on young vegetative and reproductive axes, much denser ramenta on abaxial folds; characters that are otherwise less demonstrated when found thriving over limestone and serpentine substrates. Within the same clump, saplings can attain longer internodes and leaf axes (petiole, rachis, and leaflets) dimensions ( Figure 1 C ) but will ultimately approach the described dimensions when reproductively mature.

Figures

FIGURE 1. Pinanga gruezoi Adorador & Fernando. Clustering habit showing variations in density of stems and length of petiole and rachis (A‒C). Leaf disposition and different leaflet costulation: erect (D) or slightly arching with few multi-costulate leaflets (E) or with a number of typically 2-costulate leaflets (F). Infructescence architecture showing variations in rachillae number (G‒I). Localities: Mt. Huraw, San Jose de Buan, Samar (A,D,G = the holotype Adorador 004), Barangay Vigan, Gen.Macarthur, Eastern Samar (B = Adorador 092), Barangay Tenani, Paranas, Samar (C,F,I = from Adorador 053), Sitio Arizona, Barangay Cansolabao, Hinabangan, Samar (E,H = Adorador 008). Scale bar: A = 30 cm, B = 1 m, C = 50 cm, D & E = 15 cm, F = 20 cm, G & H = 6 cm, I = 2 cm. Photos A‒I (Jiro T. Adorador).

FIGURE 2. Pinanga gruezoi Adorador & Fernando. Clustering habit (A), stem with dried infructescence axes (B), basal portion of leaf (adaxial side) including leaf sheath and petiole (C), distal portion of leaf, abaxial side (D), infructescence (E), fruit (F), longitudinal section of fruit showing ruminated endosperm (G), and staminate flower with two petals removed showing some stamens (H). Scale bar: B‒E = 8 cm, F‒G 2 cm, H = 4 mm.All drawn from the holotype (J.T. Adorador 004). Drawn by C.A.T. Rodelas.

FIGURE 3. The distribution map of Pinanga gruezoi Adorador & Fernando and closely related slender clustering species based on herbarium records.The gray-shaded area approximates the c. 150 meters below sea level bathymetry line which shows several Pleistocene Aggregated Island Complexes (PAIC) (Heaney 1986).