The microspore wall morphogenesis and orbicule ultrastructure of Isoetes were studied using electron microscopy. Microspore wall morphogenesis in five species of Isoetes (I. appalachiana, I. engelmannii, I. hyemalis, I. piedmontana, and an undescribed species from York Co., VA, USA) was studied using scanning and transmission electron microscopy. Results show that they generally have the same developmental stages in terms of microspore wall morphogenesis. The mature microspore wall consisted of four layers: perispore, paraexospore, exospore and endospore. Paraexospore formation began during the tetrad stage. The exospore was then formed between the paraexospore and the plasma membrane. During the free spore stage, two walls were formed, the perispore and the endospore. The perispore develops on the surface of the paraexospore while the endospore was formed interior to the exospore and plasma membrane. Orbicule ultrastructure of nine species of Isoetes from the USA, Canada and Syria was studied, for the first time in the genus, using scanning electron microscopy. Orbicules are minute granules of sporopollenin observed on the inner wall of the secretory tapetum and their function remains unknown. Ultrastructural variation in orbicules of the nine studied species was documented. Orbicules were very variable in both shape and size.
","abstract_html":"<p>The microspore wall morphogenesis and orbicule ultrastructure of <em>Isoetes</em> were studied using electron microscopy. Microspore wall morphogenesis in five species of <em>Isoetes</em> (<em>I. appalachiana, I. engelmannii, I. hyemalis, I. piedmontana,</em> and an undescribed species from York Co., VA, USA) was studied using scanning and transmission electron microscopy. Results show that they generally have the same developmental stages in terms of microspore wall morphogenesis. The mature microspore wall consisted of four layers: perispore, paraexospore, exospore and endospore. Paraexospore formation began during the tetrad stage. The exospore was then formed between the paraexospore and the plasma membrane. During the free spore stage, two walls were formed, the perispore and the endospore. The perispore develops on the surface of the paraexospore while the endospore was formed interior to the exospore and plasma membrane. Orbicule ultrastructure of nine species of <em>Isoetes</em> from the USA, Canada and Syria was studied, for the first time in the genus, using scanning electron microscopy. Orbicules are minute granules of sporopollenin observed on the inner wall of the secretory tapetum and their function remains unknown. Ultrastructural variation in orbicules of the nine studied species was documented. Orbicules were very variable in both shape and size.</p>","abstract_has_math":false,"creators":["Alarid, Khalid"],"institution":null,"degree_name":"Doctor of Philosophy (PhD)","degree_level":"Dissertation","degree_discipline":"Biological Sciences","degree_department":null,"school":null,"contributors":["Lytton J. Musselman","Rebecca D. Bray","Harold G. Marshall"],"advisors":[],"committee_chairs":[],"committee_members":[],"year":2008,"date_issued":"2008-01-01T08:00:00Z","date_published":"2008-01-01T08:00:00Z","updated_at":"2026-07-24T03:34:53Z","subjects":["Isoetes","Microspore wall","Orbicules","Botany","Ecology and Evolutionary Biology","Plant Biology"],"languages":[],"rights":["In Copyright. URI: http://rightsstatements.org/vocab/InC/1.0/ This Item is protected by copyright and/or related rights. You are free to use this Item in any way that is permitted by the copyright and related rights legislation that applies to your use. For other uses you need to obtain permission from the rights-holder(s).
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"]}]},{"id":"identifiers","label":"Identifiers","entries":[{"key":"dc:identifier","label":"Identifier","values":["9780549936435","https://digitalcommons.odu.edu/biology_etds/47"]}]},{"id":"additional","label":"Additional Metadata","entries":[{"key":"dc:description.abstract","label":"Abstract","values":["The microspore wall morphogenesis and orbicule ultrastructure of Isoetes were studied using electron microscopy. Microspore wall morphogenesis in five species of Isoetes (I. appalachiana, I. engelmannii, I. hyemalis, I. piedmontana, and an undescribed species from York Co., VA, USA) was studied using scanning and transmission electron microscopy. Results show that they generally have the same developmental stages in terms of microspore wall morphogenesis. The mature microspore wall consisted of four layers: perispore, paraexospore, exospore and endospore. Paraexospore formation began during the tetrad stage. The exospore was then formed between the paraexospore and the plasma membrane. During the free spore stage, two walls were formed, the perispore and the endospore. The perispore develops on the surface of the paraexospore while the endospore was formed interior to the exospore and plasma membrane. Orbicule ultrastructure of nine species of Isoetes from the USA, Canada and Syria was studied, for the first time in the genus, using scanning electron microscopy. Orbicules are minute granules of sporopollenin observed on the inner wall of the secretory tapetum and their function remains unknown. Ultrastructural variation in orbicules of the nine studied species was documented. Orbicules were very variable in both shape and size.
"]},{"key":"dc:title","label":"Title","values":["Microspore Wall Morphogenesis and Orbicule Ultrastructure of Isoetes"]}]}],"canonical_facts":{"dc:contributor":["Lytton J. Musselman","Rebecca D. Bray","Harold G. Marshall"],"dc:creator":["Alarid, Khalid"],"dc:date.available":["2019-05-20T07:00:00Z"],"dc:description.abstract":["The microspore wall morphogenesis and orbicule ultrastructure of Isoetes were studied using electron microscopy. Microspore wall morphogenesis in five species of Isoetes (I. appalachiana, I. engelmannii, I. hyemalis, I. piedmontana, and an undescribed species from York Co., VA, USA) was studied using scanning and transmission electron microscopy. Results show that they generally have the same developmental stages in terms of microspore wall morphogenesis. The mature microspore wall consisted of four layers: perispore, paraexospore, exospore and endospore. Paraexospore formation began during the tetrad stage. The exospore was then formed between the paraexospore and the plasma membrane. During the free spore stage, two walls were formed, the perispore and the endospore. The perispore develops on the surface of the paraexospore while the endospore was formed interior to the exospore and plasma membrane. Orbicule ultrastructure of nine species of Isoetes from the USA, Canada and Syria was studied, for the first time in the genus, using scanning electron microscopy. Orbicules are minute granules of sporopollenin observed on the inner wall of the secretory tapetum and their function remains unknown. Ultrastructural variation in orbicules of the nine studied species was documented. Orbicules were very variable in both shape and size.
"],"dc:identifier":["9780549936435","https://digitalcommons.odu.edu/biology_etds/47"],"dc:rights":["In Copyright. URI: http://rightsstatements.org/vocab/InC/1.0/ This Item is protected by copyright and/or related rights. You are free to use this Item in any way that is permitted by the copyright and related rights legislation that applies to your use. For other uses you need to obtain permission from the rights-holder(s).
"],"dc:subject":["Isoetes","Microspore wall","Orbicules","Botany","Ecology and Evolutionary Biology","Plant Biology"],"dc:title":["Microspore Wall Morphogenesis and Orbicule Ultrastructure of Isoetes"],"thesis:degree_discipline":["Biological Sciences"],"thesis:degree_level":["Dissertation"],"thesis:degree_name":["Doctor of Philosophy (PhD)"]},"updated_at":"2026-07-24T03:34:53Z"}