Abstract.
New morphological and developmental observations are presented of Gunnera herteri (subgenus Ostenigunnera) which is, according to molecular studies, sister to the other species of Gunnera. It is an annual dwarf (up to 4 cm long) whereas the other Gunnera spp. are perennial and slightly to extremely larger. External stem glands are combined with channels into the stem cortex serving as entrance path for symbiotic Nostoc cells. Young stem zones show globular regions of cytoplasm-rich cortex cells, prepared for invasion by Nostoc. The leaf axils contain 2–5 inconspicuous colleters (glandular scales) which can be taken as homologous to the more prominent scales of G. manicata (subg. Panke) and G. macrophylla (subg. Pseudogunnera). Foliage leaves of G. herteri have tooth-like sheath lobes which may be homologous to stipules. Adult plants have extra-axillary inflorescences arising from leaf nodes. The main stem is interpreted as a chain of sympodial units, each one consisting of a leaf and an extra-axillary inflorescence. This “sympodium hypothesis” may be also valid for other species of Gunnera. Each globular inflorescence of G. herteri contains several female flowers and 2–7 stamens at the top, perhaps equalling a single male flower. There are neither bracts nor bracteoles. The ovary is inferior, bicarpellary and unilocular. Its single hanging ovule develops into a dry and endosperm-rich seed.
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The authors thank Gisela Bauert-Reiner (Zurich) for sharing data and illustrations. Thanks to Isabelle Zumsteg and other participants of the course in plant morphology (winter term 2003/04, University of Zurich) for improving a preliminary version of the paper. We also thank P. Endress (Zurich) for valuable comments on the manuscript. Technical assistance (scanning electron microscopy) of U. Jauch (Institute of Plant Biology, University of Zurich) is gratefully acknowledged. This paper is part of a research project supported by the Swiss National Science Foundation (grant No.3100.63748) to the first author.
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Rutishauser, R., Wanntorp, L. & Pfeifer, E. Gunnera herteri – developmental morphology of a dwarf from Uruguay and S Brazil (Gunneraceae). Plant Syst. Evol. 248, 219–241 (2004). https://doi.org/10.1007/s00606-004-0182-7
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DOI: https://doi.org/10.1007/s00606-004-0182-7