Rhamnus Linnaeus (1753: 193)

Alijanpoor, Behnaz, Khodayari, Hamed, Assadi, Mostafa, Rahiminejad, Mohammadreza & Mehregan, Iraj, 2021, A taxonomic revision of Rhamnus L. and Atadinus Raf. (Rhamnaceae) in Iran, Phytotaxa 521 (3), pp. 127-158 : 129-130

1. Rhamnus Linnaeus (1753: 193) .

Lectotype: R. cathartica L., Grubov, V.I. (1949). Mонографический оБЗор рода Rhamnus L. s.l. [Monographic review of the genus Rhamnus L. s.l.] In: Schischkin,B.K. (Ed.) Trudy Botanicheskogo Instituta Akademii Nauk SSSR. Ser. 1. Flora I Sistematika Vyssikh Rastenii 8: 1–423. [Latin title: Acta Instituti Botanici Academiae Scientiarum URPSS. Ser. 1. Flora et Systematica Plantae Vasculares].

Description —Trees or shrubs, erect, ascending, creeping or prostrate on rocks, stones or cliffs, spiny or rarely without spines. Branches alternating, sometimes opposite, pubescent when young; two types of branches: long (spiny) branches ending in spines at the tip and short (scaly) branches bearing fasciculate flowers or fruits and fasciculate leaves at the end (usually scaly branches develop into spines). Buds mostly red on the spiny branches. Leaves alternate or fasciculate on short branches, polymorph in shape, herbaceous, coriaceous or membranous, with or without dendate or crenulate teeth; mostly leaves with 4-6 pairs of superficial and curved lateral nerves cream or white; base of leaves cuneate, narrowly cuneate or rounded; apex of leaves obtuse or rarely acute. Petioles unequal in each node. Stipules acute. Inflorescence mostly fasciculate or rarely a cyme. Flowers very small, in leaf axis, yellow or greenish yellow, bisexual, unisexual or polygamous, 4- or rarely 5- merous. Calyx campanulate and with triangular lobes, acute, rarely with glands, three veins; sepals deciduous. Petals very small, caduque, sometimes absent, linear or rarely broad, equal and opposite to filaments. Stamens epipetalous; anthers basifixed with inward curved. Disk very small. Ovary mostly with 2–3(–4) locular and mostly with 2–3(–4) styls. Peduncles unequal in each node. Fruits a fleshy drupe, mainly spherical, mostly with 2–3(–4) seeds, mostly with 2–3(–4) furrows. Seeds with one split.

Distribution, habitat —The species of Rhamnus are Euro-Siberian and Irano-Turanian elements and mostly grow in N, S, C & W of Iran.

The species are highly adapted to very difficult conditions such as: rocks, cliffs, high and a range of different altitudes, therefore their morphology varies greatly.

Pollination is by insects and birds with high flexibility and adaptation, have led to a large variety of these species, which they show polymorphism forms in species, diversity in leaf, a height difference of habitat and habit.

Diagnostic characters —we have determined the following charcaters for Rhamnus : yellow or greenish yellow and small flower, two types of branches: tall (spiny) and short (scaly), polymorph or unequal leaves, lateral nerves curved, petioles unequal in each node, inflorescence mostly fasciculate and rarely cymose, peduncles unequal in each node, petals opposite to filaments, anthers basifixed, fruit fleshy with 2-3 (-4) stony seeds.

Discussion —Generally in plants, perennials like trees and shrubs have a high intra population variability. Pollinating by winds, insects and birds ( Medan & Montaldo, 2005; Gulýas & Traveset, 2012; Canale et al.; 2015) led to high gene flow and consequently enormous polymorphism in shape (of course, leaves are rarely constant in each specimen), branching systems and general habits of plants, a phenomenon that resulted in a trend of splitting species among Rhamnus researchers. A comprehensive and precise examination of the herbaria materials (W, G, JE, B, TARY, IRAN and many digital herbaria) showed that some species of Rhamnu s are synonyms. For examples: R. lycioides Linnaeus (1762: 279) , R. pallasii Fischer & Meyer (1837: 46) and R. erythroxylum Pallas (1776: 722) are to be one species and their differences can be considered at the level of subsp., while R. lycioides and R. oleoides are not synonyms, because they can be discriminated based on their type specimens, shape of leaf and maturing fruit color (shape of the leaf in R. lycioides L. is linear with dark maturing fruit color, but in R. oleoides the leaf is mostly oblong and maturing fruits have red or yellow color).