The work entitled Descriptio et Adumbratio Plantarum e classe cryptogamica Linnaei quae lichenes dicuntur of George Franz Hoffmann (1760 or 1761–1826) was published in several fascicles over the period 1789–1801. They were gathered into three volumes, whose cover pages bear the dates 1790, 1794 and 1801 respectively. The work is sometimes known as Plantae lichenosae, though that phrase does not appear on the cover pages of any of the three volumes in the copy that I have seen. According to Stafleu & Cowan (Reference Stafleu and Cowan1979), the first two fascicles of volume 1 were published in 1789 and the final two in 1790. They list the date of the first three fascicles of volume 2 as ?1794 and the fourth as 1794. The fascicles of volume 3 are dated by Stafleu and Cowan as ?1801 or 1801, but we will not be concerned with that volume here.

The date given by Stafleu & Cowan for the first fascicle of volume 2, comprising pages 1–21 and Tables 25–30, is incorrect. Laundon (Reference Laundon1965: 70) stated that the original title pages of the fascicles were removed when most copies were bound, but that he had seen a photocopy of the original title page of fascicle 1, and that it bore the date 1791. This date was accepted by a few subsequent authors, for example Coppins & James (Reference Coppins and James1984) and Hawksworth (Reference Hawksworth1972), but Laundon's comment has generally been ignored.

I recently found internal evidence in an 18th century publication, Gmelin (Reference Gmelin1792), which demonstrates that fascicle 1 of volume 2 was in existence at the time that work was published. Making some allowance for the delay between Gmelin's manuscript being finished and its appearance in print, this strongly supports Laundon's claim that fascicle 1 appeared in 1791.

On page 1361, Gmelin discussed Lichen vitellinus and cited “Hoffm. pl. lichen. II. I. p. 5. t. 26. f. 1 et t. 27. f. 2”. On page 5 of fascicle 1 of volume 2 of Hoffmann's work, we find a discussion of Patellaria vitellina, with Lichen vitellinus cited as a synonym, and references to Table 26 Figure 1, and Table 27 Figure 2. On page 1378, Gmelin discussed Lichen floridus and cited “Hoffm. pl. lichen. II. I. t. 30. f. 2”, which corresponds to Hoffmann's discussion of Usnea florida on pages 19–20 of fascicle 1 of volume 2, where Lichen floridus is cited as a synonym and there is a reference to Table 30 Figure 2. On page 1378, under Lichen unranked Usnea, Gmelin discussed Lichen subvirescens and cited “Hoffm. pl. lichen. II. I. p. 7. t. 26. f. 2” which corresponds to Hoffmann's discussion of Usnea ochroleuca on pages 7–8 of fascicle 1 of volume 2. Gmelin appears to be introducing the name Lichen subvirescens Gmel. as a superfluous name for Usnea ochroleuca, and he made a slight error as Hoffmann cites Table 27 (not 26) Figure 2, but nonetheless Gmelin was clearly aware that page 7 of fascicle 1 of volume 2 of Hoffmann's work dealt with a species of Usnea.

The detail with which Gmelin cited Hoffmann's work indicates that he must have seen a copy of it. The only reasonable conclusion is that it was published not later than 1792.

It would be possible to argue that what Gmelin saw was merely a pre-publication copy of Hoffmann's fascicle. Although this possibility cannot be disproved, it seems implausible. Why on earth would Hoffmann have a fascicle ready and finished in 1791 or 1792 but wait until 1794 before publishing it? It only included 21 pages of text and 6 Tables, so publication could hardly have been difficult.

Taking the internal evidence in Gmelin's work together with the evidence already provided by Laundon, it seems beyond reasonable doubt that fascicle 1 of volume 2 of Hoffmann's work was published in 1791.

At various places in Descriptio et Adumbratio Hoffmann published names in the genus Patellaria. The first such name appeared in Hoffmann (Reference Hoffmann1789). Hawksworth (Reference Hawksworth1982: 133) argued that the name Patellaria Hoffm. was not validly published in 1789 because it was “without a separate generic diagnosis” and that the name dates from 1794. However, in the course of his discussion of Patellaria scruposa, Hoffmann (Reference Hoffmann1789: 55) included the sentence “Nomine Patellariae (quo Ehrhartus in phytophyll. usus), mihi designantur Lichenes leprosi scutellati Linn., seu crustacei Mich.. qui ex mera crusta constant, patellas proferente plus minusve cavas, margine cinctas, durioris saepe tartareae substantiae”. This is a perfectly clear diagnosis for the genus, and the name was validly published there. The ten names at species rank in Patellaria published in Hoffmann (Reference Hoffmann1789, Reference Hoffmann1790 and Reference Hoffmann1791) are therefore validly published (even though the name Patellaria Hoffm. is not itself available for use because of the later sanctioned name Patellaria Fr.: Fr.).

A few of the names at species rank in volumes 1 and 2 of Descriptio et Adumbratio merit comment. I mention here important names that offer scope for confusion or that may present problems.

Verrucaria sulphurea Hoffm. (Reference Hoffmann1789: 56) is the basionym for Lecanora sulphurea (Hoffm.) Ach. The homotypic Lichen sulphureus Hoffm. (Reference Hoffmann1784: 32), sometimes cited as basionym, is illegitimate as it is a later homonym of L. sulphureus Retz. (1769).

Verrucaria immersa Hoffm. (Reference Hoffmann1789: 58–59) is the basionym for Clauzadea immersa (Hoffm.) Hafellner & Bellem. The homotypic Lichen immersus Weber (1778), sometimes cited as basionym, is illegitimate as it is a later homonym of L. immersus Huds. (1762).

Psora saxicola Hoffm. (Reference Hoffmann1790: 82) is a nomen novum for Lichen murorum Hoffm. (Reference Hoffmann1784) nom. illeg. (later homonym) and is usually regarded as the basionym of Caloplaca saxicola. However, Hoffmann also cited in synonymy “Lichen candelaris Jacq. collect. III. p. 124. tab. 6. fig. 1”. The reference is to Wulfen in Jacquin (Reference Jacquin1791 [‘1789’]). Unfortunately, Wulfen clearly indicated that he was discussing Lichen candelarius L., the basionym of Xanthoria candelaria, which makes Psora saxicola Hoffm. an obligate synonym of that species unless Jacquin's work can be shown to have been effectively published after that of Hoffmann. Hoffmann's citation of Jacquin's work suggests that this may not have been the case (as do the dates that appear on the title pages of the two works). In the absence of such a demonstration, conservation will be required.

Patellaria silacea Hoffm. (Reference Hoffmann1790: 89) may be a synonym of Lecidea silacea Ach. (1803) but is not an obligate synonym. Acharius included within Lecidea silacea Ach. his own Lichen silaceus (Hoffm.) Ach. (1799), which is based on Patellaria silacea Hoffm., but he included Patellaria silacea Hoffm. itself with “?”. Although his statements are contradictory, it does appear that Acharius excluded the type of Patellaria silacea “by implication”.

Verrucaria contorta Hoffm. (Reference Hoffmann1790: 97–98) is the basionym of Aspicilia contorta (sometimes now known as Circinaria contorta). Hoffmann cited “Lecanora rupicola … Enum. Lich. 23. t. 6. f 3”. The reference is to his own discussion of Lichen rupicola in Hoffmann (Reference Hoffmann1784: 23–24), but as he there cited Lichen rupicola L. (=Lecanora rupicola) with “?” Hoffmann's 1790 name is legitimate and unrelated to Lecanora rupicola.

Cladonia cornuta (L.) Hoffm. (Reference Hoffmann1791: 1). Not 1794.

Patellaria vitellina Hoffm. (Reference Hoffmann1791: 5–6). Not 1794. This is the basionym of Candelariella vitellina.

Usnea ochroleuca Hoffm. (Reference Hoffmann1791: 7–8). Not 1794. This is the basionym of Alectoria ochroleuca.

Umbilicaria vellea [? (L.)] Hoffm. (Reference Hoffmann1791: 9). This is problematic. Hoffmann cited in synonymy Lichen velleus L. but with “?”. He also cited, without a question mark, the discussion of Lichen polyrrhizos in Lightfoot's Flora Scotica. Lightfoot there included Lichen polyrrhizos L. within the scope of his discussion, and although he amended Linnaeus's description, specifically stating differentia specifica emendata, he did not exclude the type of Linnaeus's name. It thus appears that Lichen polyrrhizos L. is included within the scope of Hoffmann's name. Whether or not Lichen velleus L. is included within the scope of Hoffmann's name is less clear. If Hoffmann were describing a new species then a name indicated as a “?” synonym would not be regarded as being included within the scope of the new species (Article 52 Note 1). However, I cannot find anything in the Code that deals explicitly with a corresponding situation involving an ostensible new combination. My own view is that Hoffmann did not make the legitimate combination U. vellea (L.) Hoffm. but instead published the name U. vellea Hoffm., an illegitimate superfluous name for Lichen polyrrhizos (=Umbilicaria polyrrhiza). (A reviewer of this paper considered that Hoffmann did make the combination.) If my view is correct then, since the name U. vellea has been used for a widespread species that is distinct from U. polyrrhiza, conservation will be required.

Verrucaria granulosa Hoffm. (Reference Hoffmann1791: 21). Not 1794. This is the basionym of Trapeliopsis granulosa.

Squamaria rubina (Lam.) Hoffm. (Reference Hoffmann1794: 27) is based on Lichen rubinus Lam. (Reference Lamarck1779), a name which Hoffmann cited though, unusually, he did not give a bibliographical reference. However, Lamarck (Reference Lamarck1779) has always been an obscure work, generally overlooked and rarely cited, and perhaps Hoffmann did not have access to a copy. The name may be a synonym of Rhizoplaca chrysoleuca, which is based on Lichen chrysoleucus Sm. (1791), in which case conservation would be desirable as Lamarck's epithet has priority.

Collema marginale Hoffm. (Reference Hoffmann1794: 47) is a superfluous name for Lichen marginellus Sw. (=Leptogium marginellum), a (sub)tropical species. Reports of C. marginale from temperate regions probably refer to C. crispum, following Nimis (Reference Nimis1993).

Patellaria nebulosa Hoffm. (Reference Hoffmann1794: 55) is the basionym of Moelleropsis nebulosa. It is nearly always cited incorrectly as Psora nebulosa.

Squamaria ambigua Hoffm. (Reference Hoffmann1794: 56–57) is a homotypic synonym of Parmeliopsis ambigua. It is derived from Lichen ambiguus Wulf. (1791 [‘1790’]), the name that is commonly cited as basionym for Parmeliopsis ambigua, but Wulfen's name is not legitimate, being a later homonym of Lichen ambiguus Vill. (1789). Unfortunately, Hoffmann also cited in synonymy the legitimate name Lichen diffusus Weber (1778) in Spic. Fl. Goett. 250, making Squamaria ambigua Hoffm. an illegitimate superfluous name. The nomenclature of Parmeliopsis ambigua needs to be investigated in full. Conservation may be required.