Fine Structure of Mistletoe Pollen. V. Madagascan and Continental African Viscum L. (Viscaceae)

Abstract

Pollen characters of Madagascan and continental African Viscum are described and compared to those in Asia and Australia. The subprolate, tricolporate, nonuniformly sculptured pollen of Madagascan taxa is most similar to that of Asian species. Ultrastructurally, however, the completely granular equatorial ektexine of Madagascan Viscum is most similar to that of continental African taxa. Continental African Viscum, in contrast to Madagascan and Asian species, display a wide variation in pollen shape and apertures. Pollen shape ranges from subprolate to oblate, the latter unique to Africa. The most striking feature of continental Viscum is their variability in aperture number and aperture type. Aperture number varies at both the intra‐ and interpopulational levels with such variation resolvable to the individual flower—a condition unique to the continent. The only simple (colpate) aperture type in the genus is restricted to Africa. The continental species can be divided into two species groups based on pollen characters: Group I (4 spp.) characterized by strictly tricolporate rounded convex pollen with a rodlet/granular equatorial ektexine structure and Group II (most continental species) possessing multiapertures, concave lobate shape, uniform sculpturing and granular equatorial ektexine. The African V. menyharthii, V. fischeri, V. rotundifolium and V. minimum exhibit no clear Group I or II affinities. An analysis of overall pollen characters in Viscum indicates a trend towards spheroidal shape, multiapertures and uniform sculpturing and ektexine organization. Though pollen characters suggest ties between Australia, Asia and Madagascar, they indicate an even stronger relationship between Madagascar and continental Africa, particularly eastern Africa. The relationship of the majority of African Viscum, excluding those with obvious Madagascan affinities, remains obscure. The unique palynological features of Group II species coupled with their inflorescence structure suggest an independently evolving group.

Eocene Loranthaceae pollen pushes back divergence ages for major splits in the family

“…The outstanding work on the pollen morphology of extant Loranthaceae by Feuer & Kuijt (1979 , 1980 , 1985 ) and other Santalales lineages ( Maguire, Wurdack & Huang, 1974 ; Feuer, 1977 , 1978 , 1981 ; Feuer & Kuijt, 1978 , 1982 ; Feuer, Kuijt & Wiens, 1982 ) demonstrated that most pollen produced by members of the Loranthaceae cannot be confused with pollen from other angiosperm families ( Grímsson, Grimm & Zetter, 2017 ). Grímsson, Grimm & Zetter (2017) distinguished four general types (Pollen Type A, B, C, D), of which only one (Pollen Type A) could be confused with pollen of other Santalales lineages, and would unlikely be recognised as Loranthaceae pollen if found in a fossil pollen sample.…”

The Antioxidant Activity of Mistletoes (Viscum album and Other Species)

“…Table 1 contains the species discussed in this review, including the common names, the antioxidant studies, and the related references. It is evident that so far, the studies were influenced by the prevalent presence of European mistletoe and its utilization in complementary treatments in oncology [ 120 , 121 , 122 ], though there is an abundance of research focused on antioxidant activities. Southern African countries are a potential source of native, undiscovered, exceptional species [ 123 ].…”