The U.S. Botanic Garden is the oldest continually-operating botanic garden in the country and it is located on the grounds of the Capitol building. It is open every day of the year, including federal holidays. It was built in the 19th century and has existed in its current location since 1933. There are four plants at the garden that are thought to be directly related to the Wilkes Expedition — a 19th century exploring and surveying expedition that majorly influenced the development of science in the United States. The garden also boasts numerous interesting features including a conservatory, rare and endangered plants, orchids, desert species, medicinal plants, a children's garden and jungle plants.