Final answer:
The greatest number of species in tropical forests are found among insects and plants, particularly in the biodiverse layers of tropical wet forests like the Amazon.
Step-by-step explanation:
The groups of organisms that have the greatest number of species in tropical forests are insects and plants, specifically in regions like the tropical wet forests or tropical rainforests of the Amazon. These forests exhibit high net primary productivity, supporting a vast array of biodiversity. The varying vertical layers of the forest, which include the forest floor, understory, canopy, and emergent layer, foster an environment suitable for a great diversity of life forms, particularly insect species, which thrive in these conditions. In these environments, trees are an incredibly diverse group, with between 100 and 300 species in a single hectare. The dense canopy layers and rich plant life support complex ecosystems, including numerous species of epiphytes and a variety of animal life. Furthermore, these rainforests also house a substantial number of different fungi species, contributing to the overall high biodiversity.