Euphorbia bokorensis H. Toyama & Tagane

Nuraliev, Maxim S., Toyama, Hironori, Hu, Chi-Ming, Luo, Shi-Xiao, Lyskov, Dmitry F., Kuznetsov, Andrey N., Kuznetsova, Svetlana P., Quang, Bui Hong, Binh, Tran Duc & Hoan, Duong Thi, 2022, Three new national records from Kon Chu Rang Nature Reserve, Vietnam: Euphorbia bokorensis, Glochidion geoffrayi and Lysimachia nutantiflora, Phytotaxa 574 (1), pp. 73-82 : 75-77

Euphorbia bokorensis H. Toyama & Tagane in Toyama et al. (2016: 92) ( Fig. 1 )

References: — Lim et al. (2021: 308).

Habitat and phenology: —Humid evergreen broad-leaved forests, often near streams; 400–1300 m. Flowering and fruiting in October–July.

Distribution: — Laos (Bolikhamsai: Phou Khao Khouay National Biodiversity Conservation Area), Cambodia (Kampot: Bokor National Park), Vietnam (Dak Nong: Ta Dung National Park, Gia Lai: Kon Chu Rang Nature Reserve, Lam Dong: Bao Loc).

Distribution of E. bokorensis is presented in Fig. 2 .

Studied specimens: — CAMBODIA. Kampot province: Popokwil plateau, wet slopes near stream, 800 m, 14 January 1904, C. Geoffray 357 ( P: P04462014 ) . VIETNAM. Gia Lai province: K’Bang district, Son Lang municipality, Kon Chu Rang Nature Reserve , N 14°30’42.3’’ E 108°34’23.2’’, 983 m, 26 July 2017, Bui Hong Quang, Do Van Hai, Tran Duc Binh, Duong Thi Hoan KCR 90 ( HN; herbarium of Kon Chu Rang Nature Reserve ) ; Gia Lai province: K’Bang district, Son Lang municipality, Kon Chu Rang Nature Reserve , 32 km ESE of Mang Den town, mixed forest, N 14°30’34’’ E 108°34’15’’, 1020 m, 06 April 2018, M. S. Nuraliev 2029 ( MW: MW0756573 , MW0756574 ) ; Dak Nong province: Dak Glong district, Dak Plao municipality, Ta Dung National Park , 38 km ESE of Gia Nghia city, forest on slope, N 11°51’02’’ E 108°00’35’’, 1290 m, 27 January 2021, M. S. Nuraliev, D. F. Lyskov NUR 3262 ( MW: MW0758118 , MW0758119 , MW0758120 ) ; Lam Dong province: Bao Lam district, Loc Bac municipality, 12 km WNW of Loc Thang town, in the forest, near river, N 11°44’18’’ E 107°43’22’’, 1000 m, 18 April 2013, M. S. Nuraliev NUR 836a (photo LE: LE01093252 ) ; Haut Donnaï [Lam Dong] province: near Blao [Bao Loc] agricultural station, Pnon Sapoum , forest, clay soil, 1100 m, 07 January 1935, E. Poilane 23682 ( L: L.3795101, L.3795102; P: P05545135 , P05545136 ) .

Notes.

1. Euphorbia bokorensis appears to occur throughout the Central Highlands of Vietnam. It is recorded from Kon Tum - Gia Lai and Langbian plateaus, and its occurence in Dak Lak plateau is highly probable. The findings are in line with the idea of Lim et al. (2021) that the species is widely distributed in the Eastern Indochina.

2. The Vietnamese material allows to describe certain morphological variation of E. bokorensis . The shape of leaf blade varies from oblanceolate to prominently obpandurate. Cyathophylls in some populations are significantly smaller than those in the type material: in Nuraliev, Lyskov NUR 3262, they are 1.5–3 mm long (vs. ca. 4 mm long in the protologue); in the photo record Nuraliev NUR 836a, they are scale-like, hardly exceed the involucre and do not provide showy appearance to the cyathium. Although the cyathophylls are stated to be basally fused in the protologue, they are free from each other in the specimens from Vietnam, and they are also likely to be free in the type material. Short hairs are present in the axils of cyathophylls, and sometimes also on the outer surface of the involucre. Involucre lobes are initially yellowish cream (similar to the glands), but in some cyathia they acquire red tint with age. The gynoecium also becomes reddish after anthesis in some cases.

3. It is evident that the species possesses male cyathia, which develop in the same inflorescences with the hermaphrodite cyathia ( Fig. 1B, F, G ).As far as the hermaphrodite cyathia of E. bokorensis ( Fig. 1D, E ) are protogynous (which is typical for the genus: Narbona et al. 2002), the absence of an externally visible pistillate flower at the phase of anthesis of the staminate flowers would indicate that the pistillate flower is non-functional or completely absent in a cyathium. The male cyathia are also visible in Fig. 5C, D of the protologue ( Toyama et al. 2016). The presence of male cyathia in E. bokorensis is consistent with the findings of Narbona et al. (2002) who demonstrated such functional andromonoecy to be common in Euphorbia Linnaeus (1753: 450) and especially in its perennial species. According to our preliminary observations, a vestigial pistillate flower is commonly present in male cyathia of E. bokorensis .

4. Re-examination of the type material allowed to conclude that Toyama et al. (2016) have only examined male cyathia of E. bokorensis . Here, we provide for the first time illustrations ( Fig. 1B, C, D, E ) and description of a functional (normally developed) pistillate flower of this species.

Pistillate flower glabrous, perianthless, green and sometimes becoming reddish with age; pedicel ca. 1 mm long (ovary placed just above the involucre glands or partly hidden in the involucre during anthesis); pedicel apically broadened to form a tiny collar at base of gynoecium; ovary globose, ca. 1 mm long and in diameter, longitudinally slightly 6-ridged, 3-locular; stylar column ca. 0.3–0.5 mm long; styles 3, ca. 0.5–0.8 mm long, bilobed almost to base; each style branch bent on abaxial side (facing the involucre of cyathium), apically bearing nearly globose papillate stigma.

Figures

FIGURE 1. Euphorbia bokorensis. A. Habit. B. Portion of inflorescence. C. Cyathium during male phase, side view (showing one staminate flower and a pistillate flower; other parts removed). D, E. Cyathium during female phase, oblique view (D) and longitudinal section (E). F, G. Male cyathium, top and side views. H. Cincinnus of staminate flowers, side view. Nuraliev 2029 (A, D–I) and Nuraliev, D.F. Lyskov NUR 3262 (B, C). Photos by M. Nuraliev.

FIGURE 2. Distribution map of Euphorbia bokorensis. Some of the locations on the map represent more than one specimen.