association of plant and animal from the Silurian is extremely rare
in the fossil record. The early (vascular?) plant, Cooksonia, is
associated with an Eurpterus exoskeleton. This species is one of
the earliest forms of terrestrial flora, from a time that plants
were first evolving features for land-based living. The plant was
growing from the discarded molt of a sea scorpion.
diminiative Cooksonia (a few cm) are considered to be transitional
fossils, that is, a transitional form between non-vascular bryophytes
and true vascular plants, as their fossils include the oldest known
plant to have a stem with putative vascular tissue.
Edwards, D; Davies, KL& Axe, L (1992), "A vascular conducting
strand in the early land plant Cooksonia", Nature
357 (6380): 683–685.