The flowering phenology and reproductive features of the endangered plant Disanthus cercidifolius var. longipes H. T. Chang (Hamamelidaceae)

The flowering phenology of a plant population is the sum of the individual phenologies. These individual phenologies can be subdivided into variables such as the starting date of flowering, the date of the flowering peak, and flowering duration. Various characteristics of phenology may have an important effect on reproductive success, including the starting date of flowering and flowering synchrony. However, different flowering indices may affect different aspects of phenology, and may be constrained by other plant characteristics. Disanthus cercidifolius var. longipes H.T.Chang, a plant species that only occurs in a few counties in Hunan, Jiangxi Province and Zhejiang Province and with relatively small numbers of individuals, is recorded as a 2~(nd) Class endangered species for conservation in China. The variations in morphological traits, flowering phenology and reproductive success of this species were studied. The study sites were located at Mt. Jinggang, Jiangxi Province. 50 individuals with more or less the same heights and crown diameters, in the wild population in Caijiatian, were marked and observed from 1999 to 2002. Another 50 individuals in the artificial population of Ciping, planted in 1990, and originating from Mt. Guanshan in Jiangxi Province, were also marked and observed in 2002. The flowering course of each individual was observed and the data on flowering onset, duration, mean flowering amplitude (flowers/plant/day) and end of flowering were registered. Then the relative flowering intensity and synchrony indices were calculated. The relationships between onset, duration, flower and fruit set, the correlation matrix between starting date and duration, flowering and duration, the phenology index, and fruit set in the wild population were analyzed. The results are as follows:In Disanthus cercidifolius var. longipes H.T.Chang, two axillary inflorescences are often placed opposite each other at the same node. Each inflorescence has two opposite bisexual flowers without pedicels. Each flower is ca. 15 mm in diameter and lasts 6 to 7 days. On the day of anthesis, the styles are longer than the filaments. The flowering span of the individuals is about 49 ~ 55 days. As regards flower morphology and dehiscence, the typical flowering process for a flower can be divided into 4 periods, i.e., “Pre-dehiscence” in which two filaments stretch out but without dehiscence,“Initial dehiscence” in which one or two anthers are dehisced after two days of flowering, “Full dehiscence” in which from the third to fifth day of flowering three to five anthers are dehisced and the color of the stigma changes to yellow, and the “Withering” in which all anthers are dehisced with some anthers withering and the color of some stigma changing to brown or black yellow from the sixth to seventh days.In the Caijiatian population, the time courses of flowering were similar over four years. In 1999 and 2000 the proportion of open flowers increased gradually to a peak, and then declined rapidly over the subsequent weeks. In 2001 and 2002 the proportion of open flowers increased rapidly to a peak, and then declined gradually. In the Ciping population the curve was bell-shaped. In the Ciping population flowering started on September 12~(th) in 2002, while in the Caijiatian population flowering started between September 17~(th) to 22nd. The duration of flowering in a population lasted 63~71 days. The flowering continued significantly longer in the Ciping population than in the Caijiatian population. The relative flowering intensity shows two major peaks: one from 20% to 40%, and the other from 70% to 90%. Though this phenomenon is not consistent with some other studies, it has some evolutionary significance for the studied species. The correlation analysis among onset, duration, flower and fruit set shows marked relations. There are significant negative correlations between onset and flowers, and duration and fruit set, and significant positive correlations between flowers and duration. The population with an early starting date shows