A new liverwort and hornwort flora for the northern Andes

In May 2021, the liverwort and hornwort flora of Colombia and Ecuador was finally published. After being delayed twice, certainly due to the Covid-19 pandemic, it was eagerly received and could be called an opus magnum of a long career in hepaticology. Having worked and published for over 50 years in this field, the author of this flora, S. Robbert Gradstein, is an accomplished bryologist on an international level and considered the foremost expert on Neotropical liverworts. This rather sizable book, with over 700 pages, is divided into several parts, starting with a brief introduction and a chapter on diversity and endemism. A classification precedes the taxonomic treatment, which, with about 620 pages, is the most extensive segment occupying the bulk of the book. A glossary, references, and an index to scientific names conclude the flora. The reviewer’s assessment of this book is from an Ecuadorian point of view; his knowledge of the Colombian aspects of this publication is limited. Evaluating such an extensive work like the present one is a tedious task, and hardly all observations can be referred to on a few pages; therefore, the comments are limited to some examples. In the abbreviations section, two of the twentyfour provinces of Ecuador are missing and do not appear throughout the book. In the case of Santa Elena, it might be understandable since probably neither collections nor reports of liverworts and hornworts from that province exist. For Santo Domingo de Los Tsáchilas, however, at least some liverwort species are documented; see Burghardt (2021) for a brief discussion. The classification follows Söderström et al. (2016) with minor deviations, like the distinction of Adelanthaceae and Jamesoniellaceae, the inclusion of Anastrophyllaceae in Scapaniaceae, and Southbyaceae in Arnelliaceae, among others. The taxonomic treatment comprises keys and descriptions of about 850 species, consisting of 830 liverworts and 20 hornworts, including the proposal of about a dozen new combinations, species, and subspecies. Furthermore, treatments of several genera like Acrobolbus, Lejeunea, and Lophocolea, among others, are revised. A broad morphological species concept is presented throughout the book, reflected by the proposal of about 100 new synonyms. Seventy plates illustrate almost all genera and about half of the species. Generally, the keys work well. However, the key to the Plagiochila species, including over 100 couplets, is very complex and, at times, challenging to use. Maybe this is owed to the sixty-five species involved and the extreme morphological plasticity of some common species, which key out several times. Nevertheless, it is unclear why the author did not break this key down into several shorter keys as he has done with Lejeunea, a similarly specious genus. There exists conflicting information on the status of Gongylanthus oniscoides (Spruce) Steph.