The phylloid algal genera Eugonophyllum and Archaeolithophyllum are common constituents of Virgilian and Wolfcampian reef limestones in the Hueco Mountains of Texas. These algae form bioherms and biostromes and are volumetrically important contributors to both the reef and offreef sediment budget. Reefs constructed by phylloid algae have long been considered as ecologically simple communities that lack dominant framebuilding organisms. The previously accepted constructional mechanism for reef formation has been inferred to be sediment baffling and trapping, mainly by erect phylloid algae. This new, detailed analysis of phylloidalgal growth framework, however, clearly shows that these algae were in fact capable of forming a rigid framework. Phylloid algae, mostly Eugonophyllum, together with the problematicum Tubiphytes and the red alga (?) Archaeolithoporella, formed complex, multiple encrustations (both in vivo and post mortem) and were a fundamental element of reef construction. Much of the micrite in these reefs, often regarded as a sediment, has been identified as microbialite; this microbialite is important in binding and stabilizing the initial reef framework created by the phylloid algae.
A dominant ecological succession was identified from the Eugonophyllum communities: 1. a pioneer community of phylloid algae would initially stabilize the substrate; 2. this would enable an encrusting community of mostly Tubiphytes, Archaeolithoporella, and microbialite to develop, followed by 3. a climax community of larger calcisponges.
In the Archaeolithophyllum communities, the thalli were largely constratal (organisms not substantially elevated above the substrate) and lacked any obvious microbialite association. The resultant Archaeolithophyllum communities therefore did not develop any significant depositional relief and thusformed biostromes.
