Regular Article
New Chromosome Counts in Six Strobilanthes (Acanthaceae) Species from China
2022 Volume 87 Issue 3 Pages 245-249
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2022 Volume 87 Issue 3 Pages 245-249
Chromosome numbers of six Strobilanthes (Acanthaceae) species from China have been reported for the first time: S. compacta (2n=30), S. longzhouensis (2n=30), S. reptans (2n=30), S. bantonensis (2n=32), S. hongii (2n=32) and S. retusa (2n=32). Based on reports at present, x=15 and x=16 are assumed to be the main basic chromosome numbers of Strobilanthes.
Strobilanthes Blume is one of the most diverse genera of the family Acanthaceae containing about 400 species and distributed in the tropical and subtropical regions of Asia with some species extending to the Pacific Islands (Wood 1994, Carine and Scotland 2000, 2002, Deng et al. 2006, Wood and Scotland 2009, Hu et al. 2011, Deng 2019, 2020). In China, 131 species including 59 endemic species were recognized (Deng et al. 2010a, b, c, Hu et al. 2011, Nguyen et al. 2018, Chen et al. 2019, 2020). Besides its great morphological diversity such as pollen morphology, species in this genus show different life-history patterns, some of which also produce natural indigo and are used for medicine (Bremekamp 1944, Mathew 1970, Janzen 1976, Daniel 2006, Deng et al. 2010a, Kakishima et al. 2011, 2019, Chen et al. 2019, Xu et al. 2020, Yao et al. 2021, Zhang et al. 2021). The genus is one of the most difficult groups of taxonomy and classification in angiosperm.
Chromosome numbers are effective to establish boundaries of the relationship between species, and of great significance in plant systematics and evolution (Stebbins 1971). Until now, there is very little cytological information available for Strobilanthes, the chromosome numbers of only 42 species in this genus were reported (about 10% of species in the genus) (Table 1). More studies are necessary for exploring the chromosomal evolution and systematics of Strobilanthes. The present paper is to report the chromosome counts of six species of Strobilanthes in China and to discuss the possible basic chromosome number preliminarily.
Seedlings and specimens of six species were collected from different localities of China (Table 2). The seedlings have been transplanted and kept in a greenhouse in the South China Botanical Garden, Chinese Academy of Sciences, Guangzhou, China. The voucher specimens are deposited in the herbarium of South China Botanical Garden, Chinese Academy of Sciences (IBSC).
| Taxon | Locality (Coordinate, Altitude) | Voucher | Chromosome number |
|---|---|---|---|
| S. bantonensis | Luocheng, Guangxi, China (108°34′17″E, 24°50′16.00″N, 150–270 m) | Y. F. Deng & S. Wang & Q. Yuan 27466 | 2n=32 |
| S. compacta | Yongfu, Guangxi, China (109°45′56.74″E, 25°06′17.15″N, 200–280 m) | Y. F. Deng & S. Wang & Q. Yuan 27433 | 2n=30 |
| S. hongii | Libo, Guizhou, China (107°54′35.46″E, 25°11′20.87″N, 670 m) | F. L. Chen DYF02 | 2n=32 |
| S. longzhouensis | Luocheng, Guangxi, China (106°36′01.21″E, 22°23′16.95″N, 367 m) | Y. F. Deng & Y. F. Huang 27468 | 2n=30 |
| S. reptans | Nanning, Guangxi, China (108°11′34.10″E, 22°38′40.92″N, 130 m) | Y. F. Deng & Y. F. Huang 27497 | 2n=30 |
| S. retusa | Luocheng, Guangxi, China (109°02′46.42″E, 24°54′43.60″N, 125 m) | Y. F. Deng & S. Wang & Q. Yuan 27446 | 2n=32 |
Mitotic studies were made on root tip meristems of six species obtained from seedlings in the greenhouse. Root tips were pretreated with 0.1% Colchicine and 2 mM 8-hydroxyquinoline at room temperature for 2.5 h and then fixed in Carnoy’s fluid (absolute ethanol : glacial acetic=3 : 1) at 4°C for 2–24 h. Samples were hydrolyzed in 1 M HCl solution at 37°C for 30–45 min and then stained with Carbol-fuchsin solution at room temperature for 2 h. Colored root tips were gently squashed in 45% acetic acid on slide glasses. At least 15 metaphases were examined for each species. The best metaphase images were recorded with an Olympus DP74 digital camera attached to an Olympus BX43 microscope. The photographed slide glasses were frozen by liquid nitrogen, sealed with neutral balsam, and stored in the laboratory.
Chromosome numbers of six Strobilanthes (Acanthaceae) species from China are reported for the first time here: S. bantonensis 2n=32 (Fig. 1A), S. compacta 2n=30 (Fig. 1B), S. hongii 2n=32 (Fig. 1C), S. longzhouensis 2n=30 (Fig. 1D), S. reptans 2n=30 (Fig. 1E) and S. retusa 2n=32 (Fig. 1F). All six species are diploid.
Till now, chromosome numbers of 48 species in Strobilanthes have been reported, including previously 42 species (Table 1) and in this paper six species (Table 2). The chromosome numbers vary in a wide range, which includes 2n=14, 16, 18, 20, 22, 26, 28, 30, 32, 38, 40, 42, 45, 56 and 60. The most common count is 2n=32 (in 23 species, viz. S. alata, S. asperrima, S. atropurpurea, S. bantonensis, S. barbata, S. consanguine, S. cusia, S. glutinosa, S. heteromallus, S. heyneanus, S. hirta, S. hongii, S. inflata, S. kunthiana, S. lanata, S. lurida, S. papillosa, S. retusa, S. scaber, S. spicata, S. urticifoli, S. wightiana and S. zenkeriana), then followed by 2n=30 (in 13 species, viz. S. compacta, S. dyeriana, S. flexicaulis, S. hirta, S. japonica, S. lawsoni, S. longzhouensis, S. lupulina, S. reptans, S. tashiroi, S. tomentosa, S. wakasana and S. wightiana). Other counts are scattered reports, among these reports, several species have more than two chromosome counts, e.g. S. cusia, with 2n=32 being more frequent, while n=8 and 2n=45 being relatively abnormal. It should be noted that the diversity of chromosome numbers in Strobilanthes may be caused by erroneous reports, therefore further studies are needed to confirm these reports. According to the reports at present, we consider that x=15 and x=16 are possibly the mainly basic chromosome numbers of Strobilanthes, but further studies are needed to confirm the clear variation pattern of the basic chromosome numbers in this genus.
The satellite chromosome and B chromosome may be cytological characteristics of this genus. Grant (1955) observed no more than two satellite chromosomes in S. dyerianus (2n=30). Govindarajan and Subramanian (1985) also found 6–10 satellite chromosomes in S. barbatus (2n=32), S. isophyllus (2n=20) and S. zenkerianus (2n=30). 0-2 B chromosomes are detected in S. latebrosa (Bala and Gupta 2011). However, no satellite chromosomes or B chromosomes were found in the present study. Thus, this cytological characteristic cannot be properly discussed until more counts of Strobilanthes are reported.
In addition, the life history patterns of Strobilanthes have attracted our attention for a long time. Of six species in this study, S. hongii and S. retusa were reported to be a plietesial life history (Chen et al. 2019, Yao et al. 2021). Unlike perennial polycarpic plants, plietesial species flower gregariously after several years of growth and then die. This kind of life history is known from several families but is best documented in Bamboo and Strobilanthes (Bremekamp 1944, Janzen 1976, Wood 1994, Daniel 2006, Deng et al. 2010a). This cytological study could lay a solid foundation for studying the plietesial flowering by using systematics and genomics in the future.
This work was supported by the National Natural Science Foundation of China (Grant No. 32170213, 31900182) and the Natural Science Foundation of Guangdong Province, China (Grant No. 2018A030310390).
