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The terrestrial and marine Port-Cros National (PCNP) was established in 1963; it was then made up only of the Archipelago of Port-Cros. Since 2012, it has been extended to include a vast land and sea area, including not only islands but also part of the mainland, the new PCNP (N-PCNP); the marine core area and the adjacent marine area cover approximately 120,000 ha and extend over 63 km as the crow flies, from east to west. Taxon richness is just one descriptor of biodiversity among others (e.g., functional and ecosystem diversity), and is far from being the most reliable one; however, it deserves to be taken into consideration, provided that certain prerequisites are met, because it constitutes a convenient measure of, e.g., the research effort and the diversity of habitats. The number of reported macrophyte taxa amounts to 502: 73 green algae, 316 red algae, 104 brown algae and 9 magnoliophyta and other taxa. Two new combinations are proposed: Ericaria brachycarpa var. claudiae and Gongolaria montagnei var. compressa. This gamma species diversity is far from being exceptionally high, but rather is within the norm for the Mediterranean, if we take into account the size of the area considered. The number of reported taxa per site is highly heterogeneous throughout the N-PCNP area; it is, as expected, correlated with the number of studies per site. The research effort peaked in the 1970–1980s, and then irregularly declined, which may seem surprising in this era of biodiversity launched at the 1992 Rio Summit. The exceptionally extensive database available, covering more than a century, provides the basis for a critical analysis of the concept of biodiversity, as proclaimed by the general public and the 'greens', which can be naive or biased, and of the concept of 'heritage value species', which the authors of this article consider to be a 'toxic concept', as opposed to 'ordinary biodiversity', which enables ecosystem functioning. However, this database, straddling both areas highly impacted by humans (coastal development, tourist resorts) and areas that are effectively protected, does not highlight obvious changes over time. [ABSTRACT FROM AUTHOR]