First Advisor

Clyde L. Calvin

Date of Publication


Document Type


Degree Name

Master of Science (M.S.) in Biology






Mistletoes -- Seedlings, Mistletoes -- Morphology



Physical Description

1 online resource (41 p.)


Four species of Phoradendron were examined for seedling morphology: P. bolleanum subsp. densum (on Juniperus), P. californicum (on Prosopis), P. juniperinum subsp. juniperinum (on Juniperus, P. villosum subsp. villosum (on Quercus). The main species used in the study was P. juniperinum, using the other species for comparison. The initial shoot(s) of P. juniperinum may develop from the epicotyl of the developing seedling, from adventitious buds which arise from a cushion of tissue, termed the haustorial cushion, formed beneath the holdfast, or from both positions. When shoots arise only from adventitious buds the original seedling remains attached in a lateral position, often persisting for a number of years, giving the false impression of an autoparasite establishing itself near the base of the plant. In P. bolleanum and P. villosum, initial shoots arise from the epicotyl although adventitious shoots may also develop, particularly in P. bolleanum. In contrast, P. californicum shoots are entirely adventitious in origin, and the initial seedling can frequently be seen near the center of the cluster of adventitious shoots. Cotyledons of all species in the study were found to be persistent and possess a distinctive tip probably resulting from the site of attachment to the endosperm. These distinctive, persistent cotyledons and other clearly identified morphological features, allow to readily distinguish between plumular and adventitious shoots.


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