4.3.2. Effect of Temperature on *S.* × *hainanensis* Seed Germination

Temperature is one of the key factors during seed germination. However, the response of different endangered plant seeds to temperature is also different [44]. The endangered plant *Cercidiphyllum japonicum* Siebold & Zuccarini has a low seed germination rate below 5 ◦C, and there is no significant difference between 10 ◦C and 30 ◦C [40]. The seed germination of most endangered plants, such as *Dracaena cambodiana* Pierre ex Gagnepain, *Sinia rhodoleuca* (Diels) M.C.E. Amaral and *Lumnitzera littorea*, are very sensitive to temperature, and 25 ◦C is optimal. At the same time, seeds cannot germination when the temperature is below 15 ◦C, and if it is higher than 30 ◦C [45–47]. Under laboratory conditions, the suitable temperature for *S.* × *hainanensis* seed germination was between 30 ◦C and 40 ◦C, with an optimum temperature of 35 ◦C. This condition indicates that *S.* × *hainanensis* seeds are sensitive to low temperatures, but are able to resist temperature changes within a small range. In 2008, because of extreme cold in southern China, all seedlings of *S.* × *hainanensis* were dead in the mangrove forest nature protection area of Dongzhaigang [48]. Therefore, temperature is also one of the factors limiting the seed germination of *S.* × *hainanensis.*
