BIO 10 The Vascular Plants

BIO 10 The Vascular Plants - 2009 BIO153: Lecture 10 The...

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1 2009 BIO153: Lecture 10 The Vascular Plants February 11, 2009 Origin of the vascular plants: current thinking (2006) suggests that the non-vascular plants (bryophytes) are not a monophyletic group sister taxon of the vascular plants appears to be the hornworts about 50 million years after the appearance of land plants, fossil evidence of the first vascular plants Early vascular plants: a diverse and poorly understood group. Much of our knowledge of early vascular plants comes from a large fossil deposit called the Rhynie Chert (see below). e.g. Rhyniophyta: very simple structure : bifurcating (2- way branching) stems; no leaves, no seeds, no flowers no roots (horizontal stems connected to soil by root hairs took the function of roots – anchoring the plant; likely providing nutrients: note the difference bewteen these and rhizoids in bryophytes) sporophyte dominant : sporangia borne in structures at the top of the plant – aid in spore dispersal The Rhynie Chert: a treasure-trove for plant paleontologists (in this way, analogous to the
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2 Burgess Shale for Cambrian animals, which we will see in an upcoming lecture). The Rhynie Chert is a silicified moor located about 40 km from Aberdeen, Scotland. About 400 million years ago, geysers spouted boiling hot, siliceous (silica-rich) water, preserving the plant life so perfectly that the fossils can be examined at the cellular level. Beautiful! Fossils from the Rhynie Chert: vascular tissue with lignin (strong material that permits greater growth) stomata & cuticles sporangia that split (dehisce) – spores land away from plant (dependent on moist conditions to complete the life cycle) start to see the first leaves (likely evolved independently in several groups) 2 types of leaf structure: microphylls and megaphylls Recall that we discussed how plant structure reflects adaptations to living on land. There were still unsolved problems: There are distinct competitive advantages to being taller than your neighbours if you are a plant. However, it’s hard to grow tall when you grow only via apical meristem (new cell growth only at the tips of the plant). Palm
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BIO 10 The Vascular Plants - 2009 BIO153: Lecture 10 The...

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