The garden originally received this plant as a propagule of a plant collected in the state of Nuevo León, Mexico. Bidens heterophylla was the name attached to the plant at the time, a name which the USDA Plants Database reports is a synonym of Bidens aurea. It is commonly known as Arizona beggarticks (or Arizona beggarstick), even though the vast majority of its range is in Mexico.
From what I can tell, Bidens aurea is a highly variable species. The description of the plant in the Flora of North America (see Bidens aurea) uses many parentheticals to denote that the plant's morphological properties can vary extremely from the norm, e.g., disc florets 12–30(–60+), meaning that the number of disc flowers (the ones in the centre of this composite flower) typically range from twelve to thirty, but over sixty can be found in rare plants. More evidence of variability can be seen online using an image search: Bidens aurea, including these two illustrations, 1 and 2. Despite the poorly-known scientific names on these illustrations, both are apparently synonymous with Bidens aurea (images and synonymy via the Universal Library Compositae page).
I do have to admit to being a bit skeptical that this is all one species based on the extreme differences in morphology, but I've not found anything suitably authoritative to contradict it. Particularly curious is that the FNA treatment does not describe the plant as having nearly-white ray florets, but it's within the realm of possibility that this plant was selected for that very reason (its different flower colour).
Botany / horticulture resource link: Bamboo Research through Washington State University's Extension Unit. The site leans to local resources, but also includes a number of links that are relevant anywhere bamboo will grow.