Widely-distributed plants might have mechanisms enabling them to survive in a wide range of climatic and environmental conditions. The purpose of this research was to find out whether the morphological and physiological characteristics of four plant species change with the altitudinal environments and seasons, and what are the significance of these changes to the plants. I collected healthy leaves of populations of four native widely-distributed plants along altitudinal gradients on the eastern side and western side of Central Taiwan. The four species were: Pinus taiwanensis, Alnus japonica, Miscanthus floridulus, and Plantago asiatica. The elevation intervals between adjacent sample sites were around 300-500 m. I collected leaves in Nov. of 2009, and Jul. of 2010. This study include three parts: (1) To compare leaf stable carbon (δ13C) and nitrogen isotope ratio (δ15N), and carbon (C%), and nitrongen (N%) content of populations of the four species in different altitudes. (2) To compare δ13C, δ15N, carbon (Carea) and nitrogen (Narea) content per leaf area and morphological characteristics, including leaf mass per area (LMA) and stomatal density of M. floridulus and Pla. asiatica along altitudinal gradient between two different seasons. (3) To compare the geographical distribution, and morphological traits between Pla. asiatica populations with glabrous and pubescent leaf form. According to the δ13C analysis, M. floridulus is a C4 plant, the other three species are C3 plants. The results of the first part also showed that the δ15N of A. japonica and the δ13C of M. floridulus had positive correlations with altitudes. Among three C3 species, Pla. asiatica had the lowest δ13C, indicating its long-term water use efficiency was lower than that of A. japonica and Pin. taiwanensis, or the δ13C of its carbon sources were lower. The δ15N values of A. japonica were significantly more negative than other three species, I speculated it is caused by the impact of its symbiotic rhizobium. Results of the second part revealed that leaves of Pla. asiatica populations at high altitudes had significantly higher δ13C in July than in Nov.. And a positive correlation between δ13C and altitudes was found in samples collected in July 2010. The main reason why Pla. asiatica had higher δ13C in July 2010 and in higher altitudes might due to its increases in LMA. The LMA of Pla. asiatica in July was higher than that in November, indicating that it was harder for CO2 to diffuse through the leaves in July. A positive correlation between leaf δ13C and altitude was found in western population of M. floridulus, Narea of M. floridulus also showed a generally positive correlation with altitude while LMA didn’t, it suggested that the increase of Narea was not caused by LMA , but due to more allocation of N into photosynthetic machinery. A significant correlation between δ13C and LMA was found, which suggests that LMA might be the main reason causing the variation of δ13C in M. floridulus. The results of the third part showed that Pla. asiatica individuals with glabrous, pubescent, and marginal pubescent distributed in all sample sites except for the site White Iron Gate. Further analysis revealed that there were no significant differences between glabrous and pubescent leaves in chlorophyll content, LMA, SD, δ13C、Narea and Carea.According to the result, the appearance of trichomes may have no significant effects on reducing water loss. Further study is needed to understand the functions of trichomes on leaves of Pla. asiatica.