Distribution and Anatomy of Hydathodes in Asteraceae

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Abstract
Hydathodes have been reported as rare for the Asteraceae, but published reports of guttation, water pores, and hydathodes were cultivated from .apprx. 80 genera of 10 tribes. Only a few incomplete anatomical descriptions were found. Leaf teeth with guttation droplets were removed for anatomical study from Ambrosia trifida, Arctium minus, Erigeron annuus, Eupatorium rugosum, Lactuca scariola, Rudbeckia lacinata and Silphium perfoliatum. Conspicuous xylem, but very little phloem, enters each tooth. Phloem ends well before xylem termination. Xylem diverges distally into individual files of tracheary elements separated by parenchyma. Progressively toward the tooth apex, xylem parenchyma proliferates, and successive cells are at first more elongate with increasingly sinuous walls, then shorter, broader, and lobed. The epithem beyond xylem termination resembles ordinary mesophyll chlorenchyma. The bundle sheath is variably developed but always incomplete. Water pores resemble ordinary stomata but are motly sunken, permanently open, and occur only in contact with epithem.

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