**1. Introduction**

Mangroves are various kinds of trees up to medium height and shrubs that grow in saline coastal sediment habitats in the tropics and subtropics-mainly between latitudes 25° N and 25° S [1]. Mangrove plants were comprised of true-mangrove plants and semi-mangrove plants. The true-mangrove plants were woody plants, which only grew in the intertidal zone and couldn't survive in the land. Semi-mangroves were woody plants that could both grow in the intertidal zone and in the land. The differences between the two kinds of mangroves were the specificity of living habitats of the true-mangrove and the amphibiotic living habitats of the semi-mangrove as shown in Figure 1. Meanwhile, all of them were woody plants and could grow in the specific environment of intertidal zone, and the latter was the basis of the diversified chemical constituents and biological activities of the mangroves [2].

© 2013 Zhang; licensee InTech. This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2013 Zhang; licensee InTech. This is a paper distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

The word's mangrove plants have 84 species (including 12 varieties) in 24 genera and 16 families. Of which, true mangrove plants have 70 species (including 12 varieties) in 16 genera and 11 families, and semi-mangrove plants 14 species in eight genera and five families [3]. 12 species of semi-mangroves were grown in China including *Barringtonia racemosa, Cerbera manghas*, *Dolichandrone spathacea*, *Pluchea indic, Hernandia nymphiifolia*, *Pongamia pinnata*, *Pemphis acidula*, *Hibiscus tiliaceus*, *Thespesia populnea*, *Premna obtusifolia*, *Clerodendrum inerme*, *Heritiera littoralis* [3]. Hainan province of China is most rich in semi-mangroves, where all of the 12 species were spread there. 8 species were grown in Guangxi province, 10 species were distributed in Taiwan province, 7 species were found in Fujian province, 7 species were grown in Hongkong, and 3 species were found in Macao [4].

Most semi-mangroves possessed medicinal usages were utilized as folk medicine in many provinces of China. For example, the seeds of *Cerbera manghas* were used as emetic and purgative medicine in Hainan province [1]. The leaves and branches of *Hibiscus tiliaceus* were used as the agents of clearing heat and reducing the swelling. The crude extract of *Pongamia pinnata* can effectively inhibit pathogen of the multiple evanescent white dot syndromes, and reduce mortality. The seeds of *Barringtonia racemosa* showed anti-cancer and anti-microbial activities. *Thespesia populnea* possessing relieving pain, anti-inflammatory, anti-microbial, and antioxidant activities can also protect the liver damage induced by carbon tetrachloride.

Chemical constituents isolated form semi-mangrove plants with various and unique structures including flavanoids, lignans, sesquiterpenoids, diterpenoids, triterpenoids, steroids, and alkaloids et al. For example, Abe and coworkers obtained cardiac glycosides from the seeds of *Cerbera manghas* [4]. Alis isolated some oxygenated sesquiterpenoids from the roots of *Hibiscus tiliaceus*. Some flavanoids as glabone were isolated from *Pongamia pinnata* and Wang obtained 5 thiophene derivatives from *Pluchea indic*.

Meanwhile, the biological activities of the isolated compounds were studied extensively. Some were found to have obvious biological activities. For example, cardiac glycosides showed obvious anti-cancer activity[11] and bartogenic acid can inhibit the activity of α-glycosidase and amylase [13].

In short, semi-mangrove plants played an important role in curing disease and finding new chemical entities. We highlight that it will become more and more significant to the research and development of new drugs. In this review, chemical constituents and biological activities of semi-mangrove plants were mainly regarded and they are as follows.
