РАСТЕНИЙ / PLANT ECOLOGY SOME RESEARCH ON THE GENUS CAMELLIA L. (THEACEAE) WITH REPRESENTATIVES IN VIETNAM

. Many studies have been conducted to classify the genus Camellia , yet they have not been entirely consistent. Therefore, doing research on some of the taxonomic systems of the genus Camellia will serve as the basis for the classification and arrangement of recently discovered species into a consistent system. A series of studies based on morphology as well as molecular biology techniques, the classification of pollen spores, and the analysis of leaf anatomy were examined. The systems based on morphological characteristics were inherited and widely recognized, thereby becoming an appropriate method to classify the genus Camellia with representatives in Vietnam.

the section Pierrea. Orel and Curry's system (2015) was significantly expanded. In this system, the genus Camellia was composed of up to 27 sections in which seven sections were newly created (Table 1). In addition to morphological classification studies, classification methods based on molecular biology techniques, the classification of pollen spores, and the analysis of leaf anatomy have been used. The classification results of Vijayan et al. (2009) published from the nrITS sequence analysis of 112 Camellia species gave both consensus and conflict results compared to previous morphological classification systems [50]. Although the study suggested the polyphyletic nature of the sections Camellia, Paracamellia, Pseudocamellia, and Tuberculata as well as the paraphyletic nature of the section Chrysantha, it did not support the sectional status of three small sections, Archecamellia, Piquetia, and Sterocarpus. Jiang et al. (2010) conducted a multivariate analysis of leaf shape, anatomy, and Fourier Transform Infrared (FTIR) data of 27 Camellia species with secretory structure (from the sections Archecamellia, Stereocarpus, Furfuracea, and Chrysantha according to Chang's system (1998)), together with three species from related genera, Gordonia and Tutcheria (Theaceae), to clarify some taxonomic problems [19]. This study indicated that integrated leaf characters based on leaf shape, anatomy, and FTIR data were useful in the taxonomic treatment of Camellia species with secretory structures. The results of this study also tended to support that the Chrysantha species should not be merged into section Archecamellia. Moreover, Jiang et al.  [27]. This study resulted in a clustering dendrogram of sections similar to the previous study. Thus, the analysis of leaf structure data is useful for identifying Camellia species. Lu et al.'s study (2012) complements the traditional studies that used earlier leaf morphological characteristics [27].
Classification studies on the genus Camellia in Vietnam. The earliest study of the genus Camellia in Vietnam was of the French author Lanessan (1886) with the first two species Thea dormoyana and Thea piquetiana [22]. Later, these two species were grouped into the genus Camellia. During the 20th century, the number of authors published researches about Camellia species in Vietnam increased. Gagnepain (1939) additionally published three species Thea amplexicaulis, Thea tonkinensis, and Thea flava [15]. Meanwhile, Chevalier (1919) published the next two species Thea fleuryi and Thea gilberti found in Vietnam [7]. Especially, these are also the first species of the genus Camellia in the world being described as having yellow flowers. In the monograph of Sealy (1958)  The latter period marked the presence of Vietnamese authors. The authors with typical research on the genus Camellia can be mentioned: Ho (1991Ho ( , 1999 with "Flora of Vietnam", Ninh (2002) with "Diversity of Camellia species in Vietnam", and most recently Hien (2017) with the study on the Theaceae family in "Flora of Vietnam" [16; 17; 18; 35]. Ho (1991Ho ( , 1999 classified the Theaceae family into ten genera: Anneslea, Archytea, Pyrenaria, Camellia, Gordonia, Eurya, Temstroemia, Tristylum, Adinandra, and Hartia [17; 18]. Of these, the genus Camellia has a superior ovary, an unbundled pistil, large flowers with many bracteoles like sepals, a capsule, and round wingless seeds. He also divided the Camellia into four sub-genera: Protocamellia (Stereocarpus and Archecamellia), Camellia (Camellia), Thea, and Metacamellia. The study of Ho (1999) has recorded and described 30 Camellia species that existed in the territory of Vietnam [18]. This is also considered the first comprehensive systematic announcement dedicated to Camellia species in Vietnam. However, this system was just an application of Chang and Bartholomew's system (1984) to the Camellia species in Vietnam. According to Ninh (2002), there are 50 species of Camellia in Vietnam [35]. He divided this genus into four sub-genera Protocamellia (Archecamellia, Stereocarpus, and Piquetia), Camellia (Oleifera, Furfuracea, Paracamellia, and Camellia), Thea (Corallina, Branchyandra, Longipedicellata, Chrysantha, Thea, and Longissima), and Metacamellia (Theopsis and Eriandria) [35]. Nonetheless, Ninh's research (2002) did not provide criteria for classification, as well as classification keys for taxonomic orders in the genus Camellia, and it is based on the system of Chang and Bartholomew (1984) as well. Although Ninh's system (2002) also included four genera, he classified and expanded the genus Camellia into more sections than the system of Ho (1999) ( Table 2).  Hien (2017) reported 54 species of Camellia in Vietnam [16]. His research was based on Ming's classification system (1999,2000), dividing the genus Camellia in Vietnam into two sub-genera and 12 sections. The sub-genus Thea consisted of species with clear peduncle, bracts attached to the peduncle, as well as not deciduous bracts and sepals. This sub-genus included sections Piquetia, Archecamellia, Corallina, Cylindricea, Thea, Longipedicellata, Theopsis, and Eriandria. The sub-genus Camellia was composed of species with almost sessile flowers, sepals closely attached bracts, as well as deciduous bracts and sepals. To divide it into sections, the author based on characteristics such as whether stigmas stick together or separate, the size of the leaf blade is large, medium, or small, and the bracts will soon fall or not. The number of bracts was also used to divide into sections Heterogenea, Stereocarpus, Camellia, and Paracamellia (Table 2).
There are also some other studies on the Camellia in Vietnam that can be mentioned. Ninh (2003) documented 16 species of the Camellia with yellow flowers mostly distributed in northern Vietnam [38]. However, his research does not represent a large number of Camellia species. Moreover, Ninh's publication did not accompany any descriptions or classifications according to the system. Le and Dung's collection (2016) of all yellow Camellia species in Vietnam showed that Vietnam had 34 species of Camellia with yellow flowers [23]. However, except for the Camellia with yellow flowers, their study did not report any other Camellia species, as well as classified them into the classification system.  [24]. The number of the Camellia species is very large, but the authors only based on documents without mentioning the research fieldwork. In other words, the authors did not study in detail the taxonomy of the genus Camellia.
It can be stated that the genus Camellia is the largest genus in the family Theaceae that many scientists have concerned about. Many new species were published, many methods were used, and many classification systems were applied. In particular, the classification with morphological characteristics is still considered as the main method which basically cannot be replaced, especially in Vietnamese conditions. Although there are so many classification systems of the genus Camellia in the world and in Vietnam, the ones of Sealy (1958), Chang (1981Chang ( , 1998, Chang and Bartholomew (1984), and most recently Orel and Curry (2015) are widely recognized. In Vietnam, there are three main systems including Ho (1999), Ninh (2002) and Hien (2017) ( Table  2). In which there are two systems of Ho (1999) and Ninh (2002) based on Chang's system (1998), which was extended by Orel and Curry (2015). These systems are inherited and widely used to classify the genus Camellia with representatives in Vietnam.
Conclusions. This is the first integrated study of the genus Camellia research with representatives in Vietnam. Many classification systems as well as methods have been applied to the classification of the genus Camellia. The traditional classification method based on morphological characteristics is still widely accepted and cannot be replaced in the classification of the genus Camellia both in the world and in Vietnam. Nonetheless, there were not many studies that specialized in classifying the genus Camellia was conducted by Vietnamese researchers. Thus, this study provided an overview of the studies for the genus Camellia with representatives from Vietnam, setting the stage for selecting a suitable system that will be used for the classification study of the genus Camellia of Vietnam.