This name, “Hericium erinaceum”, is a misspelling.
Many culture banks, herbarium data-bases, the National Checklist of Taiwan, the Atlas of Living Australia, a number of patents, assorted publications in analytical, medical &/or nutritional research and even a few mycologists employ the name “Hericium erinaceum (Bull. : Fr.) Pers.” Hericium erinaceum has even appeared in some papers alongside H. erinaceus. Sometimes it is even given as the accepted name. It is however an error that now comprises a substantial minority of the locatable instances of use.
The name being misspelled “erinaceum” originated in the literature as a typo appearing in Persoon’s 1818 Traite sur les Champignons Comestibles (on page 251).
Persoon had earlier employed the spelling erinaceus in 1794 (in Roemer’s Neues Magazin für die Botanik, page 153); also in 1797 (Commentatio de Fungis Clavaeformibus, page 27), and in 1801 (Synopsis Methodica Fungorum, page 560). And he did so again later, in 1825 (Mycologia Europaea, volume 2, page 153).
1818 was the only instance in any of Persoon’s works using the spelling erinaceum. Due to his respected stature as an authority and the nature of the work that it appeared within, this error has achieved some lasting power through its retellings.
His entry itself actually supports the spelling erinaceum having been made in error. In his 1818 book, all of the authorities included by Persoon had spelled it erinaceus. Persoon had cited Bulliard 1797 (see page 304 and plate 34), Paulet 1793 (see plate CXCIII) and Trattinnick 1805 (see page 191). Persoon 1818 was the first to make the error but sadly this spelling was picked up by a minor portion of active authors from that time period onward.
Due to the error either being missed or not questioned by a minor number of prominent workers across several disciplines, today a Google search will reveal that erinaceus : erinaceum are currently both in use at a 28:1 ratio, with respectively 948,000 vs 33,800 results. In some of the latter instances both names are presented to be synonyms but “erinaceum” is actually quite easy to find used in the analytical and pharmacological literature. The GBIF database shows erinaceum with 39 entries and erinaceus with 1559. It is especially common in Asian publications and databases; possibly due to databases such as the Lai 2012, Atlas of Living Australia and Cybertruffle presenting it as the accepted name for the species.
In some instances erinaceum and erinaceus have even been evaluated in studies as if they were separate taxa. Serendipitously, Park et alia 2014 compared specimens bearing both names in a molecular study and reported differences between Asian erinaceum and US erinaceus.
More work is clearly in order but the application of Latin binomials does have some clearly defined rules.
Despite that there is a peculiar hurdle in this instance. The origin of the problem arose from a leading authority, Persoon, putting a misspelling into print and this error then being repeated by a few other respected authorities. That is an unfortunate combination that easily creates long-lasting perpetuations which are often highly resistant to correction.
Competent mycologists are included among those who have used, and in a few cases still use, the name. While Cooke 1871 used erinaceus, his successors, Stevenson 1886 and Massee 1892 changed it to erinaceum. In 1978, Burdsall et alia (Mycotaxon, 7(1): 1–9) also attempted to describe a mushroom they encountered as Hericium erinaceum ssp. erinaceo-abietis.
Burdsall commented that Harrison 1973 (Michigan Botanist, 12: 177–194) had recognized Hericium erinaceum as one of the accepted Hericium species. Harrison had actually used the spelling erinaceus and never mentioned erinaceum.
Henderson 1981 helpfully made the comment that “”hedgehog” has the masculine ending “-us” even though Hericium is neuter, because “erinaceus” is a noun rather than an adjective.”
Erinaceus europaeus is the European hedgehog. In Latin, the nominative form of the noun is erinaceus and erinaceum is the accusative form.
Mycobank accordingly notes erinaceum to be an orthographic variant (i.e. a name with a spelling that entered the literature as a typo or other mistake).
Fortunately the International Code of Nomenclature for Algae, Fungi, and Plants –currently the Shenzhen Code 2018; Turland et alia (eds.)– includes some clear and simple provisions for what taxonomy is supposed to do with such orthographic variants:
61.1. Only one orthographical variant of any one name is treated as validly published: the form that appears in the original publication […]
[See the Code for the acceptable exceptions to this rule.]
61.4. The orthographical variants of a name are to be corrected to the validly published form of that name. Whenever such a variant appears in a publication, it is to be treated as if it appeared in its corrected form.
If only reality worked so simply…