These three generic names apply to different groups of species that have been found to incorporate the J or E genome, usually in combination with at least one other genome. There has been, however, some taxonomic, nomenclatural, and cytogenetic disagreement and errors in their use. The following is a review of the situation.
Lophopyrum and Thinopyrum were published on the same page of the same article in 1951 (Taxon 29:351). They are based on two series that were named by Nevski in 1936, Elytrigia sect. Holopyrum ser. Elongatae and Elytrigia sect. Holopyrum ser. Junceae. These two series were also published on the same page of the same article ( Trudy Inst. Bot. An SSSR, ser. 1,2: 83) in 1936.
Löve listed Lophopyrum elongatum (Host) Á. Löve as the type species for Lophopyrum. Its basionym is Triticum elongatum Host. In the article, Löve stated that Lophopyrum elongatum ssp. elongatum had 2n = 14 and gave its the type specimen as L. & L. Cyt. T11046 and its collection site as Yugoslavia, on the coast near Porec, Hrvatska. He did not name any other subspecies of L. elongatum in the article. Thinopyrum is based on Nevski's Elytrigia sect. Holopyrum ser. Junceae which was published on the same page as ser. Elongatae. Its type species is Thinopyrum junceum (L.) Á. Löve.
In his Conspectus, Löve (1984) stated that Thinopyrum was rhizomatous and Lophopyum cespitose. He also stated that species of Thinopyrum consisted of diploids and polyploids based on what he named the J genome whereas Lophopyrum comprised diploids and polyploids of the E genome. In 1986, he published two more generic names, Trichopyrum and Psammopyrum. The type of Trichopyrum is T. intermedium (Host) Löve [= Triticum intermedium Host] and he stated that the genus included alloploids that combined the E and St genomes. The type of Psammopyrum is P. pungens (Pers.) Á. Löve [= Triticum pungens Pers.]. He stated that its species were alloploids that combined the G [which is now called the L genome] and J genomes.Trichopyrum was based on Nevski's ser. Trichophorae. Psammopyrum was a new taxon, for which he provided a description but at no time did he write a key or provide a discussion of the how his genera differed morphologically. It needs to be remembered that he was working out of his home in California when preparing his Conspectus and other papers; he did not have access to a laboratory.
Löve stated that there are four genomes involved in these four genera: E, J, L, and what we now call St. When he named genomes, he did not attempt to cite references supporting his recognition of new genomes. Nevertheless, many of his suggestions have been supported. This is not true in this group of genera. There are two diploid taxa among the four, bessarabicum and elongatum. According to Wang (1985), they both have variants of the same genome, but Löve included bessarabicum in Thinopyrum and elongatum in Lophopyrum. Subsequent cytogenetic and molecular work has supported Wang's conclusion that the E and J genomes should be considered variants of the same genome which the International Triticeae Consortium decided to call the E genome, using superscripts to distinguish variants. Subsequent work has shown that the E genomes exists in three or four different combinations:
- As diploids and autoploids of E (some "autoploids" combine different variants of the E genome)
- In combination with the St genome
- In combination with the St and P genomes
- Possibly in combination with the L and P genomes
- Possibly in combination with the St, L. and P genomes.
- There is no evidence for a G genome.
In my experience with these taxa (which is, admittedly, limited) they all have rather similar stiff glumes and a somewhat similar aspect. On that basis, I think of them as members of the same genus. The question then becomes a matter of whether to use Thinopyrum or Lophopyrum. According to the International Code of Botanical Nomenclature, the first person to use one of the names to include the other determines future usage. In this case, the person was Dewey (1984) and he chose to use Thinopyrum. He also included T. intermedium in Thinopyrum but did not state how we would treat the species Löve placed in Psammopyrum, probably because he had not worked with them
From Kanchi Gandhi (May 23, 2009): The epithet "humidum", published in 1964, was perfectly OK. In the publication 1964, a reference is made to "A. mayebaranum Honda p.p." and to "Roegneria mayabarana sensu Keng (non Ohwi)." In 1965, Ohwi, without an explanation, changed the 1964 epithet "humidum" to "humidorum." He did not refer to his 1964 publ., nor did he provide a Latin diagnosis, refering only to "A. mayebaranum Honda p.p." Therefore, "A. humidorum" is neither a correction nor a nom. nov., but an invalidly published sp. nov. Love's 1984 "E. humidorus" may be corrected to "E. humidus". Osada's 1989 publication of E. humidus is an isonym