Ranunculus irregularifrons Dunkel, 2024

Dunkel, Franz G., 2024, Ranunculus magniflorus sp. nov. and R. irregularifrons sp. nov., (Ranunculaceae), two new species of the R. auricomus complex in Romania, Phytotaxa 678 (1), pp. 33-44 : 38-39

Ranunculus irregularifrons Dunkel sp. nov. ( Fig. 3 , 4 , 5d , 6 )

Type:― ROMANIA. Banat Mts. , District Caraș-Severin ; Oraviţa, Parcul National Cheile Nerei-Beuşniţa, ca. 1,2 km ene Ciclova Montană, rechts der Strasse zum Kloster, Gebüsch, Waldrand [right of the road to the cloister, brushes, forest edge], 320 m a.s.l., 45°01’41’’N 21°44’53’’E, 25 April 2022, F. G. Dunkel-41007 (holotype CL, isotypes GOET, M, Du-41007) .

Paratype:― ROMANIA. Banat Mts. , District Caraș-Severin ; Oraviţa, 1,3 km ene Ciclova Montană, Parcul National Cheile Nerei-Beuşniţa, rechts der Strasse zum Kloster, Laubwald, 410 m a.s.l., 45°01’26’’N 21°45’34’’E, 25 April 2022, F. G. Dunkel-41011 (Herb. Dunkel) .

Description:―Flowering shoot (slim or) gracile to robust, 17–48 cm, stalk 1.2–3.4 mm in diameter, reddish at the base, suberect to moderately patent, angle between the main and secondary axis 10–50°, flowers 2–7, enrichment shoots 0–1; basal leaves 1–5 per rosette.

Basal leaf cycle: with the exception of the third basal leaf, leaves all undivided, aperture at the base occasionally closed, usually narrow-angled; the leaf edge presents irregularly crenated in the first two, alternately crenate and crenate-serrated in the third basal leaf, in the fourth and fifth basal leaves very irregularly crenate-serrated to serrated, teeth always acute and longer or at least as long as wide.

First basal leaf 22–35 mm long, blade at the base closed to narrow-angled (0–60°), undivided.

Second basal leaf 25–45 mm long, blade at the base narrow-angled (5–40°), undivided.

Third basal leaf 35–50 mm long, blade at the base closed to narrow-angled (0–50°), divided by main incision (66–90%), cleft to divided by first lateral incision (45–70%), second lateral incision absent or up to 50%.

Fourth basal leaf 45–65 mm long, blade at the base narrow-angled (10–50°), undivided.

Fifth basal leaf 60–80 mm long, blade at the base closed to narrow-angled (0–10°), undivided.

Lowermost stem leaf divided into 7–13 segments, largest segment 30–65 mm long, occasionally stalked, oblanceolate to narrowly deltoid, 4–12 mm wide, with 6–14, usually short teeth.

Petals 3–5, 10–15 mm long, 6–12 mm wide; androclinium 0.7–0.9 mm long; receptacle ellipsoid, 3.5–4.8 mm long, 2.2–2.7 mm wide, glabrous, invervallum absent, carpellophores 0.2–0.4 mm long; fruits 2.2–3.2 mm long, beak 0.8–1.4 mm long, uncinate to involuted.

Quality of pollen: ―38.4% well developed (isotype Du-41007-7).

DNA-Ploidy:― 4x (Paratype, Oravița, Du-41011).

Etymology:― refers to the irregular and acutely serrated leaf edge, especially of the final basal leaves.

Distribution and habitat:― R. irregularifrons is only known from the Banat Mountains near Oraviţa at three different sites. Further occurences in this area are probable. It settles in deciduous forests consisting mainly of beech and hornbeam, occasionally at brushes and edges of the forest.

Specimens seen:― ROMANIA. Banat Mts. , District Caraș-Severin ; Oraviţa, Marila, beim Eingang zum Sanatorium Marila, Eichen-Hainbuchen-Wald, 670 m a.s.l., 45°03’37’’N 21°46’41’’E, 25 April 2022, F. G. Dunkel- 41015 (Herb. Dunkel) .

Notes:― Ranunculus magniflorus and R. irregularifrons belong to the Ranunculus cassubicus group sensu Hörandl & Gutermann (1998). Taxa of this informal group are characterized by generally taller size of plants, at least one cataphyll and only four almost always entire instead of seven, often divided basal leaves. Due to the restricted number and a rather homophyllous leaf cycle, their determination is often uncertain. Altogether, about 50 taxa are known mainly by descriptions of G. Marklund (1965) and R. Soó (1964, 1965). The main distribution area and biodiversity centre is situated in Northeastern and Eastern Europe. Only two species grow in Sweden ( Ericsson 2001), however, the number of taxa increases further east: e.g. ten species are reported for Finland and 17 ones for Latvia ( Marklund 1965, Evarts-Bunders 2024).

For dealing with the Ranunculus auricomus complex, it is most important to look for the type populations and characterise the whole basal leaf cycle including variability of cauline leaves and form and hairiness of receptacles. In a single plant, even the type specimen, all characters are rarely developed and the basal leaf cycle is usually incomplete.

For the area of the former Hungary, R. Soó distinguished 13 species attributable to the R. cassubicus group ( Soó 1964, 1965). In the last 20 years the author saw most of the type specimens und could collect and cultivate about two thirds of the species described by Soó. Some species, as e.g. R. heuffelii Soó (1964: 229) or R. mathei Soó (1964:229) are based on a single plant (“exemplar unicum”, Soó 1965) and need further characterization. On the other hand, most of the described species are well defined with an at least local distribution area. For instance, R. matrensis Soó (1964: 229) of the Hungarian Bükk Mountains is readily distinguishable by its nunerous almost linear verticillate cauline leaf segments even after 15 years of cultivation. Or R. reichenbachii Soó (1964: 222) doesn´t increase its small size in culture and is at least morphologically related to plants of gracile habit of the R. schilleri group (1994: 225) including R. transtibiscensis Soó (1964: 225) ( Hörandl & Gutermann 1998, Dunkel in prep.). R. magniflorus is a conspicuous taxon with the largest flowers known in this complex. The petals measure up to 20 mm, that means a diameter of more than 35 mm for a single flower.

According to the quality of the pollen grains and the the DNA content measured by flow cytometry, R. magniflorus represents a diploid and probably sexual taxa. In the whole R. cassubicus group only R. cassubicifolius W. Koch (1939: 553) is diploid and amphimctic. R. magniflorus can be added to the short list of known diploid taxa ( Dunkel 2018). A sexual reproduction mode would explain the found variability of the cauline leaf segments, here described as var. magniflorus and var. dentatus . Var. dentatus equals in some way f. longidentatus and f. stipitatus by Nyárády (1933: 101). However, both varieties grow in rather stable populations, and it is not the case that each plant is different from the other. Only rarely, intermediate forms, supposedly hybrids, are found between R. magniflorus and R. flabellifolius . By epithetical name they are called R. x auricomoides (nom. invalid.). Indeed, in this case the use of a hybrid sign seems to be appropriate.

R. magniflorus is long known at the type locality. About 1835, it was already collected by Dr. Peter Wierzbicki (1794–1847), working as a physician at Orawitza (Oravița) from 1828 until his death in 1847 ( Österreichisches Biographisches Lexikon 2020). He collected it for the Flora germanica exsiccata , edited by H.G.L. Reichenbach from 1830–1846. It is distributed as no. 1286 and 1830ff. under the invalid name R. grandiflorus , a species restricted to Eastern Turkey and Northwestern Iran. Unfortunately, the exsiccate material is variable and presents partly the hybrid R. magniflorus x flabellifolius in different expressions. Thereforere, these almost 200 years old specimens are not suited as type material.

Although R. irregularifrons grows concomitantly with R. magniflorus at all localities, a differentiation is readily possible. It differs from R. magniflorus by the irregularly and finely serrated or denticulate leaf edge with acute teeth. The lowermost cauline leaf possesses also acute teeth, number and size of the petals are less, and the receptacles present without intervallum.

The irregular leaf edge of R. irregularifrons is only found at R. circinatifrons (Marklund) Ericsson (1992: 136) . The latter differs by a coarser leaf edge with more acute teeth. R. macrantherus (1992: 144) possesses complete flowers and regular small teeth of the cauline leaf segments.

Although not all plants of the Finnish type population of R. dispar (Marklund) Ericsson (1992: 137) are so morphologically conspicuous as the two illustrated plants by Marklund (1965), R. dispar differs from R. irregularifrons by long narrowly triangled teeth of the cauline leaf segments. With few exceptions, e.g. the Polish R. szaferi Jasiewicz (1956: 87) – differing by coarse leaf edge and almost entire cauline leaf segments – almost all taxa of the Ranunculus cassubicus group possess densely pilose receptacles, however, R. irregularifrons has a glabrous one ( Jasiewicz 1956).

R. irregularifrons probably is apomictic and tetraploid. It is morphologically closely related to R. bernatskyanus Soó (1965: 400) which deviates by divided basal leaves. It is described from adjacent Serbia at Vrsac, “Várhegy”, at a distance of about 33 km. R. bernatskyanus also occurs in the Cheile Nerei-Beușnița National Park (Du-25814, Du- 40587).

Figures

FIGURE 3. Holotype of R. irregularifrons (CL).

FIGURE 4. Data sheet of R. irregularifrons.

FIGURE 5. Specimens of R. magniflorus and R. irregularifrons. a. R. magniflorus, isotype Du-25798-6. b. R. magniflorus var. dentatus, holotype (CL). c. R. magniflorus var. dentatus, Steierdorf Du-41020-2 d. R. irregularifrons, isotype Du-41007-3.

FIGURE 6. Distribution map of R. magniflorus (var. magniflorus and var. dentatus) (·), and R. irregularifrons (T).