Viscum album
mistletoe
on trees
Acer saccharinum, UK Cambridge © Maria Fremlin
galling
Malus domestica, UK, Colchester © Maria Fremlin: female inflorescence
male inflorescence

Crataegus monogyna, France, dép. Drôme, Séderon © Chris Snyers
gall
The well known mistletoe. At the point of attachment to the host tree a well defined swelling occurs, that formally must be taken as a gall.
host plants
Abies; Acer; Aesculus “carnea”, glabra, hippocastanum, x hybrida, indica, pavia; Alnus glutinosa, incana; Amelanchier ovalis; Betula humilis, nana, pendula, pubescens; Caragana arborescens; Carpinus betulus; Castanea sativa; Cornus alba, mas, ? sanguinea; Corylus; Cotoneaster integerrimus, multiflorus, nummularius, racemiflorus, tomentosus; Crataegus azarolus, crus-galli, laevigata, monogyna, orientalis, tanacetifolia; Cydonia oblonga; Cytisus scoparius (!); Fraxinus pennsylvanica; Gleditsia triacanthos; Ilex aquifolium; Juglans regia; Malus; Mespilus germanica; Picea; Pinus sylvestris; Platanus orientalis; Populus alba, balsamifera, carolinensis, nigra; Prunus dulcis, spinosa; Pyrus communis; Quercus petraea, pubescens, robur; Ribes alpinum, rubrum, uva-crispa; Robinia pseudoacacia; Rosa canina; Salix alba, babylonica, caprea, x fragilis, pentandra, triandra, viminalis; Sorbus aria, aucuparia; Tilia; Ulmus
synonyms
The Euro+Med PlantBase (2020) recognises four subspecies, next to subsp. album (on woody dicotyledons): abietis (only on Abies), austriacum (on Picea and Pinus), and creticum (geographically restricted to Crete).
references
Buhr (1964b, 1965a), Redfern & Shirley (2011a), Roskam (2019a), Varga, Poczai, Tiborcz, ao (2014b).