Fagus hohenackeriana Palib.

Denk, Thomas, Grimm, Guido W., Cardoni, Simone, Csilléry, Katalin, Schulze, Mirjam Kurz Ernst-Detlef, Simeone, Marco Cosimo & Worth, James R. P., 2024, A subgeneric classification of Fagus (Fagaceae) and revised taxonomy of western Eurasian beeches, Willdenowia 54, pp. 151-181 : 167-174

Fagus hohenackeriana Palib. in Bull. Herb. Boissier,

sér. 2, 8: 378. 1908, as “ hohenackerana ”. – Lectotype (designated here): Azerbaijan, Lesser Caucasus ,

1838–1833, R. F. Hohenacker s.n. (G [G00358037_a]

[ Fig. 13]; isolectotypes: E [E00326761], G [G00358037,

G00358037_b], US [NMNH-00409517-000001]).

– Fagus sylvatica var. macrophylla Hohen. in Bull. Soc. Imp. Naturalistes Moscou 1838: 259. 1838, pro parte, nom. nud.

– Fagus sylvatica var. macrophylla Hohen. ex A. DC. in Candolle, Prodr. 16(2): 118. 1864, pro parte.

– Fagus sylvatica subsp. hohenackeriana (Palib.) C. F. Shen, Monogr. Fagus : 60. 1992, pro parte, combination not effectively published (Art. 30.9).

Molecular diagnosis — ITS variants belonging to Lineage IV, preliminary data indicate Lineage IV ITS variants not shared with Fagus sylvatica and F. orientalis . Most diverse and heterogenous 5S-IGS pool of all species analysed so far ( Fig. 5), A Lineage variants can be more abundant than B Lineage variants (Lesser Caucasus and eastern Georgian sample) or vice versa (Greater Caucasus sample, Fig. 7); no European B variants. A Lineage variants (co-)dominated either by private to this species European A types (Hohenackeriana A1, sister lineage of Western A type) and/or the unspecific variants of the Shared A type, additional rare A-lineage types shared with the eastern sibling F. caspica ; B Lineage variants sequentially and type-wise diverse ( Fig. 6), characteristically including shared (Shared B, Western B) and (near-) exclusive (Hohenackeriana B1a, B1b, B2 and B3) types with shifting abundances between samples, a genotypic feature not found in any of the other species. Distinct isoenzyme ( Gömöry & Paule 2010) and nuclear SSR profiles ( Kurz & al. 2023), separating F. hohenackeriana and F. caspica from F. sylvatica - orientalis at k =2 and k =3. Fagus hohenackeriana and F. caspica differentiated at higher k and in the densely sampled nuclear SSR data of Sękiewicz & al. (2022; mapped in Fig. 3). [No other nuclear data available.] Lineage V plastomes, subtype not yet determined.

Morphological description — Lamina shape elliptic to obovate, usually symmetric, (60–)80–140(–200) mm, leaf index 187; leaf petiole (1–)2–9(–13) mm long; most frequent base/apex pairs “oblong very-base and blunt acute or blunt acuminate apex” and “slightly cordate or nearly oblong very-base and attenuate apex” chiefly on vegetative twigs, “acute base and apex” on fruiting twigs and sun leaves; leaf margin entire or with blunt triangular teeth (shade leaves); number of secondary veins (6–)7–12(–16); secondary venation pseudocraspedodromous, semicraspedodromous to craspedodromous in shade leaves; length of stomata (16–)20–26(–30) µm, mean 23.5 µm, subsidiary cells incomplete cyclocytic to cyclocytic or actinocytic, dispersed or in groups; cupule peduncle 5–38 mm, mean value 19 mm, length of cupule (6–)15–25(–38) mm, basal cupule appendages (1) parallelodromous, membranous brownish scales similar to bud scales, usually densely spaced ( Fig. 12C), (2) small sessile leaflets initially green but soon turning brown, spathulate to lanceolate, with dichotomous venation or (3) woody spine-like appendages similar to apical ones, apical appendages woody, spine-like.

Distribution — NE Turkey, Lesser Caucasus ( Georgia, Armenia, Azerbaijan), Transcaucasus ( Georgia, Azerbaijan), North Caucasus ( Russia).

Evolutionary significance — The isoenzyme data of Gömöry & Paule (2010) and the SSR data clustering of Kurz & al. (2023) indicate that the split between Fagus hohenackeriana (+ F. caspica ) and F. orientalis predates the split between the latter and its European sister, F. sylvatica . This is corroborated by the 5S-IGS lineages and frequent or (very) rare types shared exclusively with either F. orientalis (sister types Hohenackeriana B1b and Western B1, both sequentially distinct derivates of the commonly shared Original B types), F. sylvatica (Hohenackeriana A1, sister type of Western A) or both (Western A). The available high-resolution genetic data also indicate that F. hohenackeriana has been less isolated from its western cousins than the easternmost F. caspica and differs from the latter by an increased intra-species genetic diversity. Sękiewicz & al. (2022) found a genetic cline between the southern, western and central populations of F. hohenackeriana (eastern Pontic Mountains, Lesser Caucasus, western and central High Caucasus in Georgia) and the eastern High Caucasus populations in northeastern Azerbaijan. This finding correlates with the differential composition of the 5S-IGS pools of the three samples included here ( Fig. 6) which sets the sample from the Greater Caucasus (Racha) apart from those of the Lesser Caucasus (Borjomi + Bakuriani) and eastern Georgia (Lagodekhi): in the Racha population, hohenackeriana -specific 5S-IGS B Lineage variants co-occur with variants of a lineage also found in the western F. orientalis but very rare in the other two populations of F. hohenackeriana . In contrast, the latter share some types with their eastern sibling, F. caspica , types not found in F. orientalis or the Racha population. At this point, the genetics would fit with two evolutionary hypotheses about the origin of F. hohenackeriana . It may represent the eastern sister species of F. sylvatica + F. orientalis , sharing a common ancestor with the precursor of F. orientalis (+ later evolved F. sylvatica ), spreading across Asia Minor and the Caucasus before Anatolia and the entire eastern Mediterranean region dried out and became more continental. Or, it is the sister species of F. caspica and both species evolved from the Pontic-Hyrcanian populations of the fossil-species F. haidingeri in contrast to F. sylvatica - orientalis that evolved from the Euro-Mediterranean populations of F. haidingeri , with the fossil-species F. gussonii being the second donor. Under both scenarios, the notably high 5S-IGS heterogeneity of F. hohenackeriana could be explained by genetic legacy from further species/populations that thrived north/northeast of the modern F. hohenackeriana before the Pleistocene (north of the Paratethys and its remnant, the Caspian Sea) as well as ongoing speciation processes in the Caucasus and adjacent areas characterized by a strong topographic relief and geographic vicinity of strongly differing niches (cf. Denk & al. 2001, for the ecology and biocenoses of beech forests in Georgia).

Remarks on nomenclature — There has been some nomenclatural confusion surrounding the Caucasian-Hyrcanian beeches. Based on the initial work by Hohenacker (1833, 1838) and the taxonomic treatments by Candolle (1868) and Palibin (1908), Shen (1992) correctly considered Fagus hohenackeriana Palib. ( F. sylvatica subsp. hohenackeriana sensu Shen ; Caucasus-Hyrcanian region) different from F. sylvatica subsp. orientalis . Since no types had been cited in previous works, but both Candolle and Palibin had referred to material collected by Hohenacker, Shen chose a lectotype for F. hohenackeriana from herbarium G collected from “Azerbaijan-Talysh” Mountains ( Shen 1992: p. 166). He further listed isolectotypes from G, LE, and US. In doing so, Shen (1992) confused different collections of F. hohenackeriana , namely material collected earlier from the Lesser Caucasus s.l. (Azerbaijan part of Karabakh Mountains; Hohenacker 1833; including the isotypes selected by Shen) and later from the Talysh Mountains of Azerbaijan ( Hohenacker 1838). These collections represent geographically and genetically distinct populations and hence they cannot be lectotypes of a single species (cf. Sękiewicz & al. 2022, fig. 3 AZ_01, Lesser Caucasus, versus HZ_01, HZ_02, Talysh).

Hohenacker, a Swiss missionary based in Şuşa (German: Schuscha) in Nagorno-Karabach, started collecting plant specimens for the Esslinger Reiseverein (“Esslinger Travel Society”) in the early 1830s ( Wörz 2007). These plant specimens were sent to Germany and distributed among the members of the travel society. A first parcel of dried plant specimens, collected by Hohenacker between 1830 and 1833, contained plants from the environs of Şuşa and the mountains of Nagorno-Karabach (see Hohenacker 1833; Hochstetter & Steudel 1834). These plants were accompanied by labels with the locality information “Caucasus” (isolectotypes of Fagus hohenackeriana at herbarium Genève, G00358037; Edinburgh, E00326761; Smithsonian, US 00409517).

During a subsequent collecting trip in the summer and autumn 1834, Hohenacker collected plants from the surroundings of Lankaran and explored the montane regions of Zuvand (“district Suwant”) and Dirig/Dırığ (“district Drych”). He collected Fagus from the environs of the villages Cayrud (“Tschaioru”) and Veri (“Weri”; Hohenacker 1838). In October 1835, Hohenacker collected Fagus in southern Talysh, close to the border of Iran. In the publication arising from his collection trip ( Hohenacker 1838), he reported F. sylvatica var. macrophylla occurring “in sylvis montium Talysch prope Lenkoran, Drych, Suwant, Astara” (p. 259). The material collected during this expedition does not have “Caucasus” on the labels, but, for example “in forests in the surroundings of Lenkoran” (e.g. Hohenacker 2229 in herbarium Paris, barcode P06812042).

Hence, we here clarify the origin of the lectotype of Fagus hohenackeriana and refer Fagus populations occurring from northeastern Turkey to the Greater and Lesser Caucasus to this species. In contrast, we refer the populations originating from the Talysh Mountains and the Hyrcanian region as F. caspica (see below).

Further remarks — So far, only the spacers of the nuclear-encoded ribosomal DNA have been sequenced ( Denk & al. 2002, 2005; this study). The Caucasian populations are not covered in Jiang & al. (2022) nor in the upcoming study of Worth and co-workers. Armenian and Georgian populations have been included in the study of Paffetti & al. (2007) but their data had not the necessary quality or resolution to identify novel plastid haplotypes within the western Eurasian plastid lineage (Lineage V). Based on our experience with other Caucasian trees ( Acer , Quercus ), we expect that in-depth nuclear-genetic analyses will reveal further diagnostic traits. Screening of the nuclear loci of Jiang & al. (2022) comprising alleles reflecting the trans-Atlantic link (introgression: genes P14, P21, P54, and F289; cf. Cardoni & al. 2022) may help to decide between the two hypotheses outlined above. By extending the sample of Sękiewicz & al. (2022) to adjacent areas (Crimean, northeastern Turkish and additional Armenian and Iranian populations), it may be possible to further explore the nature of the genetic gradient found in Fagus hohenackeriana and, potentially, reveal ongoing speciation processes between the western (+ Pontic Mountains) and eastern Caucasus.

Representative specimens — TURKEY: P. H. Davis & I. Hedge D32347 (E [E00401564]); M. Tong 504 (E [E00401561]); P. H. Davis & J. Dodds 21380 (E [E00401562]); P. Sintenis 1609 (P [P06812039]); ENET 33 (E [E00318857]); [?] 828 (G [G00754880]). — LESSER CAUCASUS: T. Denk 977154 ( US [NMNH-03400173]); J. C. Solomon 20783 ( US [NMNH-03470668]); T. Denk 977229 (U [U0251466]). — TRANSCAUCASUS: T. Denk 896127 (BR [BR0000030519022]); V. Vašák s.n. (BR [BR0000030518865]); T. Denk 977011 (BR [BR0000030520585]); E. E. Gogina 47 (BR [BR0000030519084]); E. E. Gogina s.n. (E [E00401536]); S. Kuthatheladze & I. Mandenova (E [E00401545]); J. Reveal 8715 (P [P06851162]); T. Denk 896179 (P [P06812068]); T. Denk 8965 (P [P06812069]); T. Denk 977057 (P [P06851975]); T. Denk 977 (P [P06851976]); T. Denk 977222 (P [P06851978]); E. Gabrielian 12766 (E [E00401548]); V. Manakyan s.n. (E [E00401555]); P. Smirnow 312 (MW [MW0660524]); M. Barkworth & al. s.n. (NY [NY03476707]); L. N. Cilikina s.n. (MW [MW0660529]); L. N. Cilikina s.n. (MW [MW0660537]); T. Alexeenko 84b (DR [DR061665]). — NORTH CAUCASUS: B. Marcowicz s.n. (P [PI031307]); B. Marcowicz s.n. (E [E00401556]); B. Marcowicz s.n. (E [E00401557]).