noun
Refers specifically to mangroves of the family Rhizophoraceae, the typical 'true mangroves' with stilt roots. In everyday use, it may be used loosely for mangroves in general.
沖縄の海岸にはヒルギが生えている。
Mangroves grow along the coast of Okinawa.
ヒルギの林は多くの生き物のすみかだ。
Mangrove forests are habitats for many creatures.
マングローブ is the general loanword for 'mangrove' and can refer to any mangrove species, while ヒルギ is the native Japanese term specifically for Rhizophoraceae mangroves.
The origin is uncertain. The word is native Japanese, and the kanji spellings are likely ateji or later associations.