Short Communication |
Corresponding author: Ying Zhang ( zhangyingred@lingnan.edu.cn ) Academic editor: Hanno Schaefer
© 2020 Cairong Zhong, Donglin Li, Ying Zhang.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Zhong C, Li D, Zhang Y (2020) Description of a new natural Sonneratia hybrid from Hainan Island, China. PhytoKeys 154: 1-9. https://doi.org/10.3897/phytokeys.154.53223
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Here, we describe, illustrate and compare a new natural hybrid, Sonneratia × zhongcairongii Y. S. Wang & S. H. Shi (Sonneratiaceae), with its possible parent species. Based on its morphological characteristics and habitat conditions, this taxon is considered to represent a sterile hybrid between S. alba and S. apetala. In China, the new hybrid is only reported in the mangrove forest in Dongzhai Harbour, Hainan Island. It has intermediate characteristics with its parents by elliptical leaf blades, peltate stigma, terminal or axillary inflorescence with 1–3 flower dichasia, cup – shaped calyx (4–6 calyx lobes) and no petals. We also provide a key for the identification of Sonneratia species.
Sonneratia, new hybrid, Dongzhai Harbour, Hainan Island
Sonneratiaceae is a small tropical plant family consisting of only two small genera, Sonneratia and Duabanga. The inland genus Duabanga is an evergreen component of the rainforest belt, comprising two species within a more restricted range in Malaysian, Indonesia and China (
Sonneratia consists of six species and three interspecific hybrids (
The morphology of Sonneratia species presented here is based on field, vegetative and reproductive characteristics. Field traits were recorded on site, whereas vegetative and reproductive characteristics were observed and measured using fresh specimens, material preserved in 70% ethanol or press-dried specimens. Digital calipers (Mitutoyo, Japan) and a dissecting microscope with calibrated eye (Olympus, Germany) were used to describe the detailed morphological characteristics of samples. All photographs were taken in the field, i.e. in the natural habitat of the species, using a digital camera (cannon EOS RP, Japan). The morphological characteristics of Sonneratia species in Hainan Island have been summarized in a key to facilitate identification.
The results of morphometric analysis showed that S. x zhongcairongii is more similar to its parents S. alba and S. apetala than to other Sonneratia taxa (Fig.
Character | S. × zhongcairongii | S. alba [1-2] | S. apetala [3] | S. caseolaris [1-2] | S. × gulngai [1-2] | S. lanceolata [1-2] | S. ovata [1,3] | S. × hainanensis [4] | S. griffithii [3,5] |
---|---|---|---|---|---|---|---|---|---|
Leaf blades | elliptic | obovate or elliptic to ovate | narrowly elliptic to lanceolate | elliptic | elliptic | elliptic | broadly ovate | elliptic or broadly elliptic | obovate or suborbicular |
Leaf apices | rounded mucronate | rounded | rounded mucronate | apiculate, mucronate | apiculate, mucronate | apiculate, mucronate | rounded | rounded | obovate mucronate |
Leaf base | attenuate oblique | attenuate oblique | attenuate oblique | attenuate oblique | attenuate oblique | attenuate oblique | reniform | broadly cuneate | cuneate |
Peduncle | terete | terete | terete | terete or tetragonous | terete | terete or tetragonous | terete | terete | terete |
Calyx lobes | 4~6; inner often green | 6~7(8); inner often red | 4; inner often green | 5~7; inner often red-streaked | 5~7; inner often green | 5~7; inner rarely red-streaked | 6; inner often red at base | 6; inner often red | 6-7: inner often green |
Petals | absent | white[6], linear-spathulate | absent | red, linear | red, linear | red, linear, rarely double | absent | white | white (absent)* |
Stamen | white | white | white | red, rarely white | red | white | white | white | white |
Stigma | Mushroom-like, to 5~7 mm wide | capitate but not expanded, 1~3 mm wide | Mushroom-like, to 7~10 mm wide | capitate but not expanded, to 3 mm wide | capitate but not expanded, to 1.7 mm wide | capitate but not expanded, to 3 mm wide | capitate but not expanded, to 3 mm wide | capitate but not expanded, to 3 mm wide | capitate but not expanded, to 3 mm wide |
Inflorescence | terminal or axillary, 1-3(-5)-flowered dichasia | terminal cyme occur either solitarily or in groups of three | terminal cyme from branch axis | terminal or axillary, 1-3(-5)-flowered dichasia | terminal or axillary, 1-3-flowered dichasia | terminal or axillary,1(-2)-flowered dichasia | terminal cyme or solitarily or in groups of three | terminal cyme 1-3(-5)-flowered dichasia | terminal cyme 1(-2)-flowered dichasia |
calyx (hypanthium) | cup-shaped | cup-shaped | flat-expanded | flat-expanded | cup-shaped | flat-expanded | cup-expanded | cup-shaped | cup-shaped |
Fruit | Not developed | Width = corolla width | Width = corolla width | width 5 mm > corolla width | Width = corolla width | width 5 mm > corolla width | width 6-8 mm > corolla width | width 5 mm > corolla width | Width = corolla width |
Seeds | Not developed | falcate | falcate | angular irregular | angular irregular | angular irregular | rounded irregular | angular irregular | angular |
Dongzhai Harbour, mangrove forest Hainan Island, China (Fig.
Trees, evergreen, 10–12 m tall, highly branched (Fig.
The hybrid is currently found only in Dongzhai Harbour within an area of 48 m2, mangrove forest, Hainan Island, China.
The hybrid grows in a mangrove forest.
The new hybrid flowered from the beginning of March to the end of October.
The new hybrid S. × zhongcairongii was collected only from the mangrove forest in Dongzhai Harbour. At this site, only two individuals were observed.
To date, only three hybrids including S. × zhongcairongii have been reported in the genus Sonneratia. As with S. × zhongcairongii, other two hybrids have restricted location in the cross distribution of each parents (
To better distinguish amongst species belonging to the genus Sonneratia, we created a classification as shown in Table
1 | Petals present | 2 |
– | Petals absent | 3 |
2 | Petals white | 4 |
– | Petals red | 5 |
3 | Stigma capitate but not expanded | 6 |
– | Stigma mushroom-like | 7 |
4 | Leaf blades obovate or elliptical to ovate | S. alba |
– | Leaf blades elliptic or broadly elliptical | S. × hainanensis |
5 | Fruit calyx flat-expanded, fruit width > corolla width by 5 mm | 8 |
– | Fruit calyx cup-shaped, Width = corolla width | S. × gulngai |
6 | Leaf blade apices rounded | S. ovata |
– | Leaf blade apices obovate mucronate | S. griffithii |
7 | Flat-expanded calyx, fruit present | S. apetala |
– | Cup-shaped calyx, fruit absent | S. × zhongcairongii |
8 | Leaf blade apices rounded | S. caseolaris |
– | Leaf blade apices apiculate, mucronate | S. lanceolata |
This study was supported by National Science Foundation of Hainan Province, China (grant numbers 318MS176; 319QN214); the National Natural Science Foundation of China (grant number 41776148).