Rafflesia mixta Barcelona, Manting, Arbolonio, Caballero & Pelser, 2014

Barcelona, Julie F., Manting, Muhmin Michael E., Arbolonio, Romel B., Caballero, Rolly B. & Pelser, Pieter B., 2014, Rafflesia mixta (Rafflesiaceae), a new species from Surigao del Norte, Mindanao, Philippines, Phytotaxa 174 (5), pp. 272-278 : 273-276

Rafflesia mixta Barcelona, Manting, Arbolonio, Caballero & Pelser , sp. nov. – Figs. 2 & 3 .

Type: — PHILIPPINES. Mindanao: Caraga Region, Surigao del Norte Province, Mainit Municipality , Barangay Cantugas , loco dicto Sarawag , lowland evergreen forest interior, on steep slopes with loose soil, 9°34’38.9” N, 125°27’7.3” E, c. 622 m, 7 June 2014, Arbolonio & Caballero 5 (female flower; holotype: PNH; female flower; isotype: Mindanao State University - Iligan Institute of Technology ) .

Rafflesia mixta differs from R. mira in having flowers with substantially sparser and smaller warts on the perigone lobes, a more or less uniformly reddish orange or maroon instead of yellowish-orange disk with longer and dimorphic instead of polymorphic processes,

and a relatively smaller diaphragm aperture through which the disk is only partially visible.

Mature flower buds to 19–22 cm diam. Flowers 40–55 cm diam. when fully open, 8.5–15 cm high, male and female flowers similar in size, 1.25–2.25 kg fresh weight. Cupule to 11.5 cm diam.; bracts imbricate, orbicular, largest c. 13 cm long, 14.5 cm wide. Perigone tube 10–15 cm high. Perigone lobes 5, broadly orbicular, 9.0– 19 cm long, 12–23 cm wide, reddish brown, margins entire to irregularly sinuate; warts powdery white becoming concolorous with background with age, relatively sparse compared to other Philippine Rafflesia species , largest ones concentrated at the base of perigone lobes, mostly wider than long, to 0.6 by 1.5 cm wide, variously shaped, and becoming smaller and rounder towards the margin of perigone lobes, interspersed by smaller warts of less than 1 mm diam. Diaphragm 15–25.5 cm diam., c. 3 mm thick, 5–7.2 cm wide from aperture rim to base of perigone lobe, velvety and ferruginous throughout, devoid of warts or other forms of ornamentation ( Fig. 3A ), windows absent; aperture 6.5–14.25 cm diam. in its widest dimension, rim white surrounded by a thinner dark red band, aperture to disk diameter ratio less than 1 (0.72–0.95). Disk 9–11.5 cm diam., to 2 cm thick towards center, nearly flat but with a prominently raised margin; margin c. 1.5–2.5 cm tall, shallowly incised or crenulate; disk only partially visible through the aperture, reddish orange to maroon, darker near the margin, similar in color underneath. Processes 22–29, more or less regularly disposed, largest c. 3.5 cm long and 2 cm wide at base, apex glabrous, tinged white in buds and fresh flowers, dimorphic between a central and peripheral/outer zone; processes of the central zone 6–9, conical; processes of the outer zone 16–20, somewhat radially flattened at base and more clearly so at apex, to 2 cm wide at base, to 1.5 cm wide at apex ( Fig. 3A, C & D ). Column short, less than 1 cm long, c. 5 cm broad. Corona c. 2 cm wide, smooth, slightly paler in color than the disk above, glabrous except in anther sulci of male flowers where sparse, white, filiform hairs are present similar to those on the annulus interior. Annulus exterior less than 1 cm broad, 9–10 cm diam., smooth, yellowish and sparsely hairy towards the interior, becoming golden to reddish orange and glabrous towards the exterior. Ramenta polymorphic, maroon, concolorous with perigone tube, those on the floor of perigone tube filiform, to 2 cm long, dense, becoming stouter and branched or cleaved apically towards the diaphragm aperture ( Fig. 2C & E ). Male flower without vestigial ovary; anthers 19 or 20, semi-globular, c. 5 mm diam., deeply immersed in anther sulci that are c. 1 cm long and c. 8 mm wide ( Fig. 3E ). Female flower without vestigial anthers, disk becoming dome-shaped as it develops into fruit in senescent flowers, ovary c. 4 cm high, c. 8.5 cm wide, slightly lunate in longitudinal section ( Fig. 3B ). Mature fruits not seen. Host plant is Tetrastigma sp. (Arbolonio et al. 3, CHR, Mindanao State University - Iligan Institute of Technology, PNH).

Additional specimens examined (paratypes): — The following specimens were collected from the same site as the holotype and isotype, the first two probably infected the same host and may represent the same plant as the holotype: 9°34’38.9” N, 125°27’7.3” E, c. 622 m, 5 April 2014, Barcelona with Manting, Arbolonio & Caballero. 4042 (immature male bud; CAHUP), 4043 (mature male bud; CHR); 9°34’39.7” N, 125°27’6.6” E, c. 615 m, 5 April 2014, Barcelona 4044 with Manting , Arbolonio & Caballero (male flower; PNH), Barcelona 4045 with Manting, Arbolonio & Caballero (immature male bud; Central Mindanao University Herbarium) .

Diagnostic characters: — Rafflesia mixta is one of five Philippine Rafflesia species with flowers that grow larger than 35 cm in diameter: R. leonardi Barcelona & Pelser (2008: 224) , R. mira , R. schadenbergiana , and R. speciosa . Of these, the range of flower sizes of R. speciosa from Negros and Panay ((31–) 45–56 cm diam.; Barcelona et al. 2009) is perhaps most similar to that of R. mixta (40–55 cm). Rafflesia speciosa also resembles R. mixta in the presence of perigone warts that are generally less prominent than in the other three large-flowered species, although they are more sparsely distributed in R. mixta . Both taxa can be easily distinguished by, amongst others, features associated with their processes. These are monomorphic and cone-shaped in R. speciosa and dimorphic in R. mixta (cone shaped processes in the central zone of the disk and apically flattened processes in the outer zone). The processes of R. speciosa are usually crowned with golden tufts of trichomes that are absent in R. mixta . Furthermore, the disk of R. speciosa is always paler in color than the diaphragm, whereas this is the opposite in R. mixta . The diaphragm of R. speciosa is ornamented with whitish warts whereas it is uniformly colored and lacks ornamentation in R. mixta .

The range of flower size of R. mixta also overlaps with that of R. leonardi from northern Luzon (25.5–50 cm diam.; Barcelona et al. 2011), but R. leonardi flowers have a diaphragm aperture that is much wider than the diameter of the disk (1.2–1.5 ratio), whereas it is narrower than the disk in R. mixta flowers (0.72–0.95 ratio). Furthermore, R. leonardi , when at all present, has fewer processes (up to 16 vs. 22–29) and these are considerably shorter in length (up to 1.2 vs. up to 3.5 cm; Barcelona et al. 2011).

Rafflesia schadenbergiana of central and southern Mindanao has larger flowers (52–80 cm diam.; Barcelona et al. 2011) than R. mixta . Its conical processes are very similar in size and shape as those of R. mixta , but the outer whorl of processes is less flattened at the apex. The warts on the perigone lobes and diaphragm of R. schadenbergiana are variously shaped, often coalescent, and prominently raised.

Overall, R. mixta is most easily confused with R. mira and, in fact, to an untrained eye, the resemblance between these species is quite striking. Both have a similar range of floral dimensions, a uniformly rust-colored diaphragm devoid of warts and other ornamentations, a very faint scent, and polymorphic ramenta. However, R. mixta markedly differs from R. mira in its sparser and smaller variously-shaped warts on the perigone lobes, longer (up to 3.5 vs. up to 2.3 cm long), and dimorphic disk processes in two zones (polymorphic and in four zones in R. mira ), and a nearly uniformly-colored, reddish orange to maroon disk that is only partially visible through the diaphragm opening (entirely visible and yellowish-orange with a dark-red margin in R. mira ).

Etymology: — Named for its flower morphology, which shows a combination of features characteristics of three other Philippine Rafflesia : the shape and size of the conical processes of R. schadenbergiana , the floral size and sparsely distributed perigone warts of R. speciosa and the overall resemblance, floral size, faint scent, and diaphragm and ramenta morphology of R. mira .

Distribution and habitat: —Only known from the type locality in the mountains east of Barangay Cantugas, loco dicto Sarawag, Mainit Municipality, Surigao del Norte Province, in the Caraga Region (Region XIII) of Mindanao. The area flanks the northeast side of Lake Mainit and is an important watershed of Mainit Municipality. The habitat is a relatively intact lowland evergreen forest on very steep slopes with loose soil. This site is some 250 km away from populations of Rafflesia mira of Compostela Valley ( Fig. 1 ) to which it is most similar in general morphology. Whereas R. mira plants inhabit the elevational range of 900–1300 m, R. mixta is found at much lower elevation (584–622 m).

Conservation: — Rafflesia mixta is only known to infect three Tetrastigma host plants within a 30 m radius at the type locality, which is c. 100 m uphill from a recent kaingin (slash & burn farm) of more than half a hectare and an abandoned small-scale mine. Hence, this species is Critically Endangered (CR B1ab(iii,iv); D; IUCN 2001; Fernando et al. 2008). Rampant mining activities in the Caraga Region pose a major threat to the watershed area in which R. mixta is found. In our opinion, it is in the best interest of the people of Mainit, and especially the Mamanwa tribe, that this area be legally protected. In this way, future management of this biodiversity-rich forest can be decided upon by all its stakeholders. Currently, efforts are being initiated by the DENR and the local governments of Mainit Municipality and Barangay Cantugas as well as the Mamanwa tribe to declare the forest of Cantugas a Critical Habitat and Community Watershed.

Figures

FIGURE 1. Distribution map of Rafflesia in Mindanao, Philippines. White circle: type locality of R. schadenbergiana, presumably locally extinct. An unknown small-sized Rafflesia species was collected from Mt. Matutum in the 1980s (Central Mindanao University Herbarium!; Barcelona et al. 2009b).

FIGURE 2. Rafflesia mixta. A. Open flower. B. Open flower with Ms. Mary Love P. Sanchez for scale. C. Longitudinal section through an immature male bud showing ramenta distribution. D. Rafflesia mira, open flower. E. Rafflesia mixta, thin section of a male bud showing details of ramenta (lower right: perigone tube, upper left: diaphragm). A. Arbolonio & Caballero 5 (isotype, collected 4 days after this photograph was taken). B. Barcelona 4044 with Manting, Arbolonio & Caballero. C & E. Barcelona 4043 with Manting, Arbolonio & Caballero. D. Photo courtesy of Department of Tourism, Region 11.

FIGURE 3. Rafflesia mixta.A. Open male flower showing partially visible disk processes through the diaphragm aperture.B. Longitudinal section through a female flower showing ovary. C. Bud with perigone lobes removed to show the short column, blade-like processes, and ramenta. D. Disk with regularly distributed processes in two zones. E. Anthers underneath the disk. A. Barcelona 4044 with Manting, Arbolonio & Caballero. B. Arbolonio & Caballero 5. C–E. Barcelona 4043 with Manting, Arbolonio & Caballero.