Streblus, a very unfamiliar genus to me, belongs to Moraceae where about five species could be found in Hainan but none in Hong Kong. I only managed to find immature fruits of S. taxoides during my visit to Hainan in late May. Moraceae usually produces syncarp like Ficus or Artocarpus but some of the genera also produces drupe like Streblus.
There is very few information and pictures of Syzygium fluviatile (Myrtaceae) available on internet and books after some intensive search. It might be because of its globally narrow distribution as it is probably a Chinese endemic. Even so, it is only found in three provinces in China, including Guangxi, Guizhou and Hainan according to Flora of China. However, a rapid biodiversity survey report prepared by KFBG, Hong Kong, stated that this species is endemic to Hainan. Indeed, it is a very common streamside shrub in Hainan based on my own observation. The specific epithet "fluviatile" means existing in or about rivers which is very true.
Scutellaria javanica is a large Scutellaria species which could reach up to 1 m tall and has relative large flowers among other Scutellaria species. In China, it is only distributed in Hainan which is a nationally uncommon species. It can also be found in Indonesia and Philippines, suggesting it is a tropical species. Its type specimen was from Java which gives its specific name, javanica.
Canthium horridum is a common weedy shrub in Hainan Island but a rare species in Hong Kong. Rubiaceae is a tropical family which is very diverse and predominant in Asian tropical regions. Identifying Rubiaceae is not difficult in field by its opposite leaves, persistent stipules and lack of latex. Some of its members are armed with thorns though it is quite uncommon.
Hydnocarpus hainensis is a restrictedly distributed species in Southeast Asia which is ranged from southern China to Vietnam. The Chinese population is mostly restricted in Hainan Island. It is listed as vulnerable according to the IUCN Redlist though its status might be outdated. However, as it is mainly found in low altitude in mountaneous regions where deforestation is serious, it still constitutes certain level of conservation importance.
Turraea pubescens (Meliaceae) was found along streams in low altitude in Hainan. It is a small shrub with simple leaves and medium-sized flowers. It therefore didn't give impression of Meliaceae to me in the field as most of the known species are having compound leaves and relatively small flowers. Its roots are widely harvested and used as medicines by the locals.