Garcinia longifolia is a wild relative of Mangosteen, G. mangostana, under Taxon group 4, according to the Maxted et al. (2006) Taxon Group concept.

Following the synonymizing of Rheedia under Garcinia (Sweeny 2008), R. longifolia Planch. & Triana was reduced to an illegitimate homonym of G. longifolia Blume. In 2018, G. leptophylla was validated as the correct name of R. longifolia (Bittrich and Marinho 2018), however, prior to this, some institutions curated R. longifolia Planch. & Triana under G. longifolia Blume. As such, some data sources incorrectly indicate this species occurs in South America (GBIF 2023). This assessment follows the view that this species is endemic to Java, as per POWO (2023).

Garcinia longifolia is a small tree endemic to Java, western Indonesia. Its preferred habitat is inferred to be montane rainforest, and its altitudinal range is suspected to be between 0–1,800 m asl. It is only known from Gunung Salak and based on an area of habitat analysis, its extent of occurrence and area of occupancy are estimated to be between 4–80 km², falling within the threshold values for the Critically Endangered category under criterion B1 and ranging from Critically Endangered to Endangered categories under criterion B2. It is likely rare, having only been collected twice and not since 1881; however, it is not known if it has been actively searched for since this date. No numerical population data are available and the lack of life history data makes it difficult to assess the potential impact of historic deforestation on Java. If it occurs at higher elevations on Gunung Salak, while likely to have experienced a historic habitat loss and subsequent population decline, a stable population could be protected within Gunung Halimun Salak National Park. The species is not known to be severely fragmented or subject to extreme fluctuations. While the park faces some pressures from small scale illegal mining and agricultural encroachment, the current scope and severity of these threats are unlikely to threaten the species within a time span that is of relevance to its extinction risk. If it occurs on steep slopes or near volcanic craters it could also be threatened by landslides or geothermic gas releases. Depending on its population restriction, and the impact of any threats, it is considered plausible that this species could qualify for extinction risk categories ranging from Critically Endangered to Least Concern. Due to this uncertainty, pending further research, it is assessed as Data Deficient.

This species is endemic to Java, western Indonesia (POWO 2023), known from only two collections on Gunung Salak. These collections are historic and lack accurate locality data; as such, they are considered a single location. The altitudinal range of this species is unknown, however, Garcinia often occur at low to mid elevations (Stevens 2007) and within the protologue it is described as occurring within mountains (Blume 1825). As such, it is suspected that its elevation range is between 0–1,800 m asl based on the distribution of lowland and lower montane forest in Java (Whitten et al. 1997). Using an area of habitat analysis following Brooks et al. (2019), its extent of occurrence and area of occupancy are estimated to be between 4–80 km².

Known only from two herbarium specimens both collected from the same area, it has not been collected since 1881 and is likely rare. Java experienced significant deforestation in the 19^th and 20^th centuries, and it is estimated that, as of 1982, only c. 57% of montane forest remained (Smiet 1990). The lack of life history data makes it difficult to assess the potential impact of past deforestation on its population size. If it occurs at higher elevations on Gunung Salak, while it likely would have experienced a past decline, its population could now be relatively stable within the Gunung Halimun Salak National Park. Beyond this, no population data are available and the current population trend is unknown. It is not known whether the population is severely fragmented or subject to extreme fluctuations. It is not known if it has been actively searched for in recent periods. Further research on this species' population dynamics is recommended.

Garcinia lonigfolia is a small tree growing to 12 m tall and occurs in montane regions (Blume 1825). Its habitat is unknown but based on contextual information in the protologue, its preferred habitat is believed to be montane rainforest, though it could also occur in lowland rainforest. Beyond this, the habitat and ecology of this species is poorly known. Further research into this species' ecology and life history is recommended.

The lack of detailed life history and ecological data makes it difficult to assess the present and past threats to this species. The majority of remaining montane forest on Gunung Salak is found within the within Gunung Haliman Salak National Park. Deforestation was active within many protected areas in West Java up until 2007 (Higginbottom et al. 2019). However, since then rates have decreased significantly (Higginbottom et al. 2019), and it is estimated that there has only been a 0.7% loss in tree cover across its range since 2007 (Global Forest Watch 2023). While illegal mining activities and agricultural encroachment are ongoing within Gunung Halimun Salak National Park (Soehartono and Mardiastuti 2014, Sardjo et al. 2022), the current rates of these are believed to be negligible and are not considered likely to affect the extinction risk of this species within a short time period. If it occurs on steep slopes or near volcanic craters, it could also be threatened by landslides or geothermic gas releases. Further research into potential threats is recommended.

Garcinia longifolia Blume is a wild relative of Mangosteen, G. mangostana, under Taxon group 4, according to the Maxted et al. (2006) Taxon Group concept. Research is recommended to determine whether the species represents an appropriate candidate for use in gene transfer to this crop.

The single known locality of this species is within Gunung Halimun Salak National Park (UNEP-WCMC and IUCN 2023) and while no specific conservation measures are in place, passive conservation is assumed in this area. The species is reported to be held in two ex situ plant collections (BGCI 2023), however, given the recent taxonomic revision of this species, it is suspected that this listing may be erroneous. Genetic information is not held in any ex situ depositories (National Center for Biotechnology Information 2023, Genesys 2023). The collection and deposition of genomic data in an ex situ collection is recommended.