Melastoma malabituin Agcaoili, Barcelona, & Pelser, 2020

Agcaoili, John Michael, Barcelona, Julie F. & Pelser, Pieter B., 2020, Melastoma malabituin (Melastomataceae): a new species from northern Luzon, Philippines, Phytotaxa 435 (1), pp. 25-32 : 26-30

publication ID	https://doi.org/ 10.11646/phytotaxa.435.1.3
persistent identifier	https://treatment.plazi.org/id/2E6887EE-B756-AC6D-30C4-C1F880C5EB23
treatment provided by	Felipe
scientific name	Melastoma malabituin Agcaoili, Barcelona, & Pelser
status	sp. nov.

Treatment

Melastoma malabituin Agcaoili, Barcelona, & Pelser View in CoL , sp. nov. ( Figs. 1 View FIGURE 1 , 2B, E, F, H View FIGURE 2 & 3D–G View FIGURE 3 )

Type:— PHILIPPINES. Luzon, Isabela Province, San Mariano , Barangay San Jose , 16° 55’ N, 122° 12’ E, ca. 300 m, 7 March 1997, Wilkie, Argent, Mendum, Pennington, Reynoso, & Gaerlan 29023 (holotype: E!; isotype: L!). Duplicates of this collection (i.e., isotypes) were also circulated as Argent, Gaerlan, Reynoso PPI No. 20023 ( BRIT photo!, K!, L!, PNH photo!) GoogleMaps .

Diagnosis: — Melastoma malabituin is similar to M. yiianthum K.M.Wong ( Wong 2016) in having penicillate hypanthium emergences, and petioles and internodes with pilose indumentum. Melastoma malabituin , however, has hypanthium emergences with notably longer stalks, 5-veined instead of 7-veined leaves, longer pedicels, and a narrower hypanthium.

Description (prepared from the type specimens and from field notes and photos of a plant from Echague, Isabella Prov., by Agcaoili, Penetrante, & Rodelas ( Fig. 1 View FIGURE 1 ) that was not collected):—Shrub up to 3 m tall. Young branches 4-ridged and slightly quadrangular in cross section, internodes 13–105 x 1–4.5 mm; indumentum pilose, of more or less erect, dark-red, thin, unbranched trichomes of unequal length and up to c. 3.5 mm long, at least present on the apical four internodes. Older internodes terete, glabrescent. Nodes swollen, 1–7 mm wide. Leaves simple, opposite. Petioles adaxially flattened or slightly caniculate, 5–31 mm long, pilose, densely covered with the same trichomes as found on the young branches. Leaf blades ovate to elliptic to narrowly ovate or narrowly elliptic, (3–)5–16.2 x (1–) 2–6.1 cm, length/width ratio 1.9–3.6; base (rounded to) attenuate; margin denticulate and ciliated at each tooth; apex acuminate; nerves 5, adaxially sunken; adaxial surface sparsely but regularly strigose, trichomes simple and c. 1 mm long, basal part of midvein with 1–2.5 mm long erect simple trichomes; abaxial surface sparsely pilose with erect simple trichomes of unequal lengths (0.2–3 mm) on veins; chartaceous to slightly coriaceous. Inflorescence a sessile terminal cyme of (1–)3(–5) flowers. Flowers 5-merous, 25–42 mm diam.; bracts narrowly ovate, 5–9 x 2–5 mm, with erect and simple up to 2 mm long trichomes. Pedicels 8–13 mm long, pilose with similar trichomes as found on young branches. Hypanthium narrowly campanulate, 10.1–17 x 4–10 mm, surface with penicillate emergences but otherwise nearly glabrous; stalks of emergences 3–5 mm long, glabrous or with few up to 1 mm long smooth bristles along their length, green; apical bristles of emergences up to 8 mm long, mostly longer than the stalks of the emergences, smooth, dark-red. Sepals linear, 5–15 x 1 mm, indumentum of single or clustered dark-red trichomes similar to the bristles at the apex of the hypanthium emergences. Petals broadly obovate, 12–20 x 8–20 mm, distal portion of margin serrulate and ciliate, apex rounded with a stellate emergence, pink. Stamens dimorphic; outer stamens: filaments c. 7.5 mm long and yellow, connectives c. 1.8 mm long with two c. 1 mm long ventral appendages and yellow, anthers c. 6.5–8.5 mm long, yellow but red at apex; inner stamens: filaments as long as those of the outer stamens and yellow, connectives c. 0.3–0.4 mm long with two c. 0.8 mm long ventral appendages and yellow, anthers c. 6.5–8.1 mm long, yellow. Ovary ovoid, 5-locular, c. 8 mm long, apex crowned with bristles of various length up to 5 mm long; style c. 20 mm long, pinkish-red; stigma green. Mature fruit not observed.

Type specimens: —The type specimens of M. malabituin were originally collected as Wilkie, Argent, Mendum, Pennington, Reynoso, & Gaerlan 29023, but some of these were subsequently renumbered using Philippine Plant Inventory (PPI) numbers (Argent, pers. comm.). It is unclear why different collector names (i.e. Argent, Gaerlan, Reynoso) were used on the labels of the renumbered specimens (Argent, pers. comm.). According to the label information on the PPI-numbered specimens, eight duplicates were made. We examined four of these (E, K, L —two duplicates) and viewed photos of duplicates at BRIT and PNH. It is unclear where the two remaining duplicates are located.

Discussion: — Meyer (2001) listed three species of Melastoma with penicillate hypanthium emergences (terminology sensu Wong 2016; ‘stellate’ in Meyer 2001) in his revision of the genus. Two of these— M. beccarianum Cogniaux (1891: 356) from Borneo and M. saigonense ( Kuntze 1891: 247) Merrill (1948: 212) from Indochina and Thailand —were included as accepted species and one from the Philippines as a ‘species dubium’ ( Otanthera luzoniensis ).

Melastoma malabituin resembles M. beccarianum in the strigose adaxial leaf surface, but this indumentum is much less dense ( Fig. 2H View FIGURE 2 ). On its abaxial leaf surface, M. beccarianum has, in addition to erect simple trichomes, larger and more appressed lanceolate and scale-like trichomes with a serrated margin ( Fig. 2A View FIGURE 2 ; Wong 2016). These also form the indumentum of its internodes and petioles and hide most of their surface ( Fig. 2C View FIGURE 2 ; Wong 2016). Melastoma malabituin entirely lacks these scale-like trichomes. Instead, its internodes and petioles have a pilose indumentum of long and slender trichomes ( Figs. 1F View FIGURE 1 & 2E, F View FIGURE 2 ). The leaves of M. beccarianum are narrower than those of M. malabituin ((0.7–)1.5–2(–3.2) vs. (1–) 2–6.1 cm; Wong 2016). In addition, the pedicels of M. beccarianum are shorter (2–4 mm; Wong 2016) than the pedicels of M.malabituin (8–13 mm). The stalks of the hypanthium emergences of M. beccarianum are very densely set with short simple bristles ( Fig. 3A View FIGURE 3 ; Fig 2A View FIGURE 2 1 View FIGURE 1 in Wong 2016). These are either absent or very sparse on the emergence stalks of M. malabituin ( Figs. 1D, E View FIGURE 1 & 3D, G View FIGURE 3 ). Both species can also be distinguished by the size of their petals and stamens. The petals of M. malabituin are 12–20 mm long, whereas those of M. beccarianum measure 20–32 mm ( Meyer 2001, Wong 2016). The outer stamens of M. malabituin have filaments that are c. 7.5 mm long (vs. (6–) 11–12 mm; Meyer 2001, Wong 2016) and anthers that are 6.5–8.5 mm long (vs. c. (8–) 9–12 mm; Meyer 2001, Wong 2016).

Melastoma saigonense is easily distinguished from M. malabituin by the very dense pilose to lanuginose indumentum on both surfaces of the leaves ( Fig. 2G View FIGURE 2 ; vs. adaxially sparsely strigose ( Fig. 2H View FIGURE 2 ) and abaxially sparsely pilose, Fig. 2B View FIGURE 2 ). These leaves are also somewhat smaller than those of M. malabituin (2.3–7.6 vs. (3–) 5–16.2 cm long; Meyer 2001). Furthermore, both species differ in details of their hypanthium emergences. Those of M. saigonense have papillate bristles ( Fig. 3B View FIGURE 3 ), whereas the emergence bristles of M. malabituin have smooth surfaces ( Fig. 3G View FIGURE 3 ). In addition to penicillate emergences, Melastoma saigonense also has simple trichomes on its hypanthium, but these are absent in M. malabituin . Although Meyer (2001) mentioned that the emergences of M. saigonense have stalks that are 3–5 mm long, those of the type specimen (Kuntze 3962, K!) are almost sessile or up to 1.5 mm long (vs. 3–5 mm long in M. malabituin ).

Otanthera luzoniensis is only known from the type specimens, which were collected from Mt. Alzapan (Ramos & Edaño BS 45719, A photo!, BM!, K!, NY photo!, P photo!, US photo!) and lack petals and stamens. It is not entirely clear where exactly Mt. Alzapan is located, but herbarium label information of specimens of other species collected from this mountain in various herbaria (e.g., A, B, K, NY, P, US) suggests that it is either in present-day Nueva Vizcaya or in the adjacent provinces of Aurora or Quirino. This area is just south of Isabela Province, from which M. malabituin is known, and likewise part of the Sierra Madre mountain range. This species is superficially similar to M. malabituin , but also O. luzoniensis is different from the new species in characters of its indumentum. The trichomes on the internodes and petioles of O. luzoniensis are appressed (i.e. strigose; Fig. 2D View FIGURE 2 ) instead of erect ( Figs. 1F View FIGURE 1 & 2E, F View FIGURE 2 ) and they are shorter (most <1 mm) than those of M. malabituin (up to 3.5 mm). In addition, they are early caducous and the internode indumentum of O. luzoniensis is consequently much less dense than that of M. malabituin ( Fig. 2D View FIGURE 2 ). The same type of trichomes that are found on the internodes of O. luzoniensis is also found on the abaxial and adaxial surfaces of its leaves, as well as on the adaxial leaf surface of M. malabituin ( Fig. 2H View FIGURE 2 ). However, the abaxial leaf surface of O. luzoniensis is nearly glabrous, with just a few scattered trichomes that are mostly found on the main veins, whereas M. malabituin has a more prominent pilose (instead of strigose) indumentum ( Fig. 2B View FIGURE 2 ). The stalks of the penicillate hypanthium emergences of O. luzoniensis are of about the same length as those of M. malabituin , but the apical bristles of the former species are shorter than the stalks ( Fig. 3C View FIGURE 3 ), whereas most of M. malabituin are longer ( Figs. 3D, G View FIGURE 3 ).

Of the species described since the revision of Melastoma by Meyer (2001), M. yiianthum is the only species with penicillate hypanthium emergences. This Bornean species resembles M. malabituin in having internodes and petioles with a pilose indumentum of long and slender trichomes, but differs from this species in, amongst others, much shorterstalked hypanthium emergences (0.5–1 vs. 3–5 mm long; Fig. 2A 2 View FIGURE 2 in Wong 2016) and 7-veined instead of 5-veined leaves ( Wong 2016). Moreover, the pedicels of M. yiianthum are shorter than those of M. malabituin (2–3 vs. 8–13 mm long) and the hypanthium of the former is subglobose to bowl-shaped ( Wong 2016), whereas the new species has a narrowly campanulate hypanthium ( Figs. 1D View FIGURE 1 & 3D, F View FIGURE 3 ).

Etymology: —The epithet ‘malabituin’ refers to the Tagalog word for ‘resembling a star’ (mala- = like/resembling/ similar to; bituin = star). This is in reference to the penicillate hypanthium emergences of M. malabituin .

Phenology: —This species was observed flowering in March (type specimens), and February and September (Agcaoili pers. obs.). In September, some plants with young fruits and flower buds were also observed.

Distribution and ecology: —This species is only known from a remnant of secondary lowland forest in the municipalities of Echague and San Mariano. In Echague, it grows on dry but moist rocky substrate in a semi-shaded area just beside a contributory canal of the Ilagen/Ilagwen River (loco dicto), which runs through both municipalities. Some small populations were also observed in an open and exposed area, where they co-occur with other Melastomataceae species.

Conservation status: —The municipality of Echague was home to a logging site during the 1970–1980s. Large parts of the forest were cleared and converted for different land uses (e.g. agricultural, residential). The rampant development of the area still continues. Despite this, several important pioneer and climax plant species still survive in forest fragments. These include species of Dipterocarpaceae , Euphorbiaceae , Fagaceae , Moraceae , and Urticaceae . Seventeen individuals of M. malabituin were observed in Echague.Anthropogenic activities in the area will undoubtedly put this small population at serious risk of extinction. In addition, it is unknown if the population in San Mariano still exists. However, the extent of the total distribution and the number of populations of M. malabituin are presently unknown. We therefore consider its conservation status to be Data Deficient (DD; IUCN 2017).