**3.4 Rare plants conservation**

Out of 321 plant species studied from this region, three plant species have been listed in the IUCN Red list [22], *Cycas balansae* Warb. as Near Threatened (NT), *Cycas bifida* (Thiselton - Dyer) K. D. Hill as Vulnerable (VU) and *Aquilaria crassna* Pierre ex Lecomte as Critically Endangered (CR). That species also is listed by the Vietnam Red book as *C. balansae* Warb. as Vulnerable (VU), *C. bifida* (Thiselton - Dyer) K. D. Hill as Vulnerable (VU), and *A. crassna* Pierre ex Lecomte as Endangered (EN) [22] and another species were listed by the Vietnam Red book and the Decree 06/2019/ND-CP of the Government of Vietnam [23, 24] (**Table 3**, [6, 22–24]).

*C. balansae* Warb. was distributed in Vietnam and Lao, south of China, and north of Thailand [25]. Plants grow under the forest canopy, on limestone mountains, at an altitude of about 100–500 m. Beautiful tree planted as an ornamental [26]. The studies suggest small population sizes of cycads brought about by fragmentation of their habitats, over-exploitation, and the increasing number of inbred individuals within populations [27].


#### **Table 2.**

*List of medicinal plant combinations used by Tay ethnic people.*

*C. bifida* (Thiselton - Dyer) K. D. Hill is distributed in Vietnam, China (southern Guangxi and eastern Yunnan provinces), Southeast Asia, and Australia. The number of mature individuals ranges from 10.000 to 12.000 and the altitude range is 100 to 300 meters above sea level. The sap of cycad treats ulcers, but the megasporophyll of cycad is known to treat pain relief [28]. The Tay people use the leaf of this species to treat bone marrow disease.


#### **Table 3.**

*List of rare medicinal plants for conservation.*

*A. crassna* Pierre ex Lecomte is endemic to the Indochina region and is known to be used in diverse Southeast Asian traditional medicine systems to treat infectious and inflammatory diseases, arthritis, and cardiac disorders [29]. The Tay people use the leaf of this species to treat cure colds and abdominal pain. According to the Dictionary of Vietnamese Medicinal Plants, *A. crassna* Pierre ex Lecomte has a beneficial effect on digestive diseases, anti-diarrhea, anti-emetic and antipyretic [27]. In the research Ethnobotanical study on medicinal plants used by local Van Kieu ethnic people of Bac Huong Hoa nature reserve, Vietnam reported the Van Kieu people use the root of this species to treat fever and abdominal pain [30]. Studies on *A. crassna* Pierre ex Lecomte revealed that the extracts from leaves and stems possess antioxidant, antimicrobial, cytotoxic, antipyretic, analgesic, antiischemic, laxative, and digestive properties [31–35].
