Short Communication New distribution record of the endemic and critically endangered Giant Staghorn Fern Platycerium grande (Fee) Kunze (Polypodiaceae) in central Mindanao

Platycerium grande (Fee) Kunze is an endemic, Critically Endangered species of fern in the Philippines. The known distribution of this species remains limited at present and its population is threatened by various anthropogenic threats especially for ornamental collection. In our recent survey, we found high abundance of this species in Central Mindanao, southern Philippines. It can be distinguished from other species belonging to the genus Platycerium through its frond’s vegetative leaf which is symmetrical with two equally long main lobe. Based on literatures, the known distribution range extend from Zambaonga, Lanao, and Davao (Mt. Apo); and our recent records extends the known distribution of this species in Kalamansig, Sultan Kudarat and South Upi, Maguindanao suggesting this species may still be around in other areas within the known range, however, the species may remain narrowly distributed as multiple threats to this species continue to persist.


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Platycerium Desv is a distinct genus under Polypodiaceae, and is distinguished by the morphological structure of its frond. The species under this genus is distinguishable by its frond dimorphism, formation of a basket of base fronds and the vegetative frond that is divided dichotomously (Hennipman & Roos 1998). This taxa mainly grow in a more or less open canopy and are among the most frequent vascular plant epiphytes in subtropical to tropical lowland forests with 15 to 18 known species. There are two known species in the Philippines, viz.: Platycerium coronarium (König ex Müller) Desv and Platycerium grande (Fèe) Kunze (Copeland 1958;Hennipman & Roos 1998). The previously mentioned species can be identified from the latter by its foliage frond which is asymmetrical and its soral patch that completely covers the fertile lobe. Of these two species, P. grande is endemic to the Philippines (Amoroso & Amoroso 2003) and is closely related to P. holttumii distributed in Indochina (Kreier & Schneider 2006).
Platycerium grande also known as the Giant Staghorn Fern was recorded in Mindanao specifically in Zamboanga, Lanao, and Davao (Mt. Apo), however, Copeland's (1958) report from Mt. Cristobal in Luzon could be possibly in error (Pelser et al. 2019). Hennipman et al. (1979 stated that the specimen used to complete the description of this species was taken from the wild of Davao and traced in Cebu then brought to Leiden and Kew.

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Its unique and peculiar structure makes this species valuable as an ornamental and attractive plant for collectors and poachers (Darnaedi & Praptosuwiryo 2003). As a matter of fact, P. grande and other species in the genus are highly-prized ornamental species. Consequently, coupled with habitat changes in its native range, continuous over exploitation, and its poor propagation success (Amoroso & Amoroso 2003) this species is currently assessed as critically endangered (Fernando et al. 2008). In this paper, we report the new distribution records of P. grande in localities in Mindanao Island, Philippines.

Methods
The study was conducted in the two provinces of Central Mindanao: Sultan Kudarat and Maguindanao, southern Philippines. The province of Sultan Kudarat is situated in the Soccsksargen region in the southwestern part of Mindanao. Kalamansig is one of its municipalities which is situated at approximately 6.554 0 N, 124.052 0 E. On the other hand, area in Maguindanao where P. grande exist is the municipality of South Upi which lies at about 7.017 0 N, 124.176 0 E (Fig. 1).
Purposive sampling was done. Survey was conducted from the months of April 2018-April 2019 in various areas of Kalamansig and South Upi. Three barangays in Kalamansig, Sultan Kudarat were identified -Barangays Paril, Limulan and Poblacion and two in South Upi, Maguindanao -Barangays Kuya and Poblacion. The actual number of individuals were counted and recorded. To confirm the identity of the species, morphological characteristics of the species were examined such the base and vegetative fronds and the soral patch. These are the morphological characteristics by which the two species of Platycerium in the Philippines can be distinguished. Identification is further supported by the work of Copeland (1958), Hovenkamp et al. (1998) and Philippine plant list website. Furthermore, a map was generated using QGIS application.

Results and Discussion
Platycerium grande was found thriving along national road for both areas in Kalamansig, Sultan Kudarat and South Upi, Maguindanao, however, individuals of this species in Kalamansig, Sultan Kudarat were seen in an agricultural area planted with coconut. The species was identified based on its morphological characterization in which the lower part of the base frond is strongly wavy on the margin (sinouse margin), upper part spreading and forked equally, and foliage fronds are symmetrical, with two equally long main lobes, each with a wide, horizontal soral patch and two lateral pendulous forked lobes. Soral patch of P. grande is semicircular and occupies the undersurface of the foliage fronds (Image 1). These are the diagnostic characteristics to identify the species as Platycerium grande (Copeland 1958;Hennipman & Roos 1998;Aspiras 2010). The species was found to be thriving in an open area at an elevation of 6.69-662.71 m and observed to be commonly attached on coconut and huge trees along national roads. The wild population of Platycerium grande is presently scarcely known. It can, however, be seen in home gardens or botanical gardens. But recently it was found out to be abundantly thriving in areas of Sultan Kudarat and Maguindanao. A total of 212 individuals were recorded from the three barangays of Kalamansig, Sultan Kudarat and 30 individuals from South Upi, Maguindanao (Table 1).
Coconut served as the phorophyte of most recorded individuals of P. grande in Kalamansig, however, many individuals were noticed to be thriving on an individual tree of Albizia saman. This might be due to fact that areas where the species was seen is an agricultural landscape which is almost planted with coconut. Its point of attachment on a coconut tree starts from 2m from the ground up to the point almost reaching the top of the tree where the fruit are located. It was also

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documented that individuals growing on trees coexist with a Drynaria sp.
It was previously mentioned that most individuals recorded were on coconut trees, however, fewer in number compared with those on huge trees (Image 2). P. grande attached on coconut ranges from 1-5 individuals wherein huge trees harbors up to 30 individuals per tree. This might be due to the absence of branches on coconut trees which gives mechanical support to this plant being an epiphyte.
Result of this study will help to substantiate the distribution of Platycerium grande in this part of the country given that very little literature is available on its distribution in the Philippines (Pelser et al. 2019). It is presumed that more individuals can be found in the two areas and neighboring places if comprehensive surveys are conducted. Moreover, findings of this study will also be of use in reassessing its status and in the implementation of appropriate conservation strategies. Furthermore, discovering new locations of P. grande is an avenue for more in-depth studies of this endemic and critically endangered species of fern.