ch23

Chapter 23

SEED PLANTS: ANGIOSPERMS

All flowering plants are classified in a single Division, Magnoliophyta . Angiosperms are commonly known as “flowering plants.” This division contains the greatest number of living species a bout 2!"###. They are characteri$ed by producing flowes  a synapomorphy that unifies them. %irst appeared in the Cretaceous about &3# million years ago. The angiosperms have developed numerous methods of interaction with animals that are  beneficial to both. They have developed many antiherbivore compounds that defend them against plant eating animals and parasites. !"ARA!TERISTI!S O# ANGIOSPERMS • • • • • •

•

'oody 'oody or herbaceous. (resence of vessels. A)ial parenchyma* parenchyma cells mi)ed with vessels and tracheids. (roduce flowers. (ollinated by wind or animals. +ouble fertili$ation, egg - sperm  embryo and 2 polar nuclei - sperm  endosperm. eeds enclosed in a fruit.

E$OL%TION O# T"E #LO&ER 

Angiosperm stamens and carpels developed from the gymnosperm sporophylls. /ymnosperm sporophylls are flat and spirally arranged and microsporophylls never occur with megasporophylls. %lowering plants with flat spirally arranged flower parts are thought to be most ancient. 'asal angiospe(s  have flat stamens without distinct filament and anther portions arranged in spirals and their sporogenous tissues 0microspore mother cells1 form relatively large prominent internal masses. •

 Amborella  Amborella ymphaeales Austrobaileyales and agnoliales.

4n most angiosperm carpels the edges of sporophyll grow shut against one another sometimes leaving a suture sometimes not. These are called )lose* )apels . Closed carpels develop into fruits that enclose the e mbryos as they develop into seeds. Carpels in the basal angiosperms are leaf5like* resembling young leaves whose blades have not yet opened. 'asal angiospe(s  lack stigma and style* instead the ovary edges have rows of secretory hairs that secrete a thick li6uid that both seals the seam and functions as a stigmatic surface.

The stigmatic surface acts as a selector of pollen grains eliminating pollen from another species or preventing self5fertili$ation. self5fertili$ation.

T"E #LO&ER 

The flower is a reproductive shoot or branch. 4t has four parts arranged in whols or circles on a stalk or peduncle. The parts of the flower are the sepals 0caly)1 petals 0corolla1 sta(ens  and )apels . Sta(ens  consist of a fila(ent  and an anthe. !apels are also referred to as pistils . They consist of an ovay  a style and a stig(a.

%lowers may be borne singly or in clusters called inflorescence. %lower parts are considered modified leaves. The ability to produce bise)ual flowers must have h ave occurred very early. All flowering  plant clades including basal angiosperms have the megasporophylls located above the microsporophylls on a single a)is. The fusion of carpels into a single structure 0pistil 1 and the fusion of petals into one corolla 0sy(petaly 1 and floral parts that are bilaterally symmetrical rather than radially symmetrical 0+ygo(ophy 1.

DO%'LE #ERTILIATION

4t is characteristic of flowering plants and universally present.

+ouble fertili$ation results in the formation of a *iploi* +ygote  and a tiploi* en*ospe( . The female gametophyte or embryo sac has an egg n-)le-s  and two pola n-)lei . 7ne sperm fertili$es the egg nucleus and forms the $ygote 2n. Another sperm 8oins the two polar nuclei forming the triploid 03n1 nutritive tissue called the en*ospe( . +ouble fertili$ation also occurs in gnetophytes but there is a disagreement if it is a case of  a shared ancestral feature 0sy(plesio(ophy 1 or convergent evolution 0ho(oplasy 1. OT"ER ANGIOSPERM APOMORP"IES

Study Table Table 23.1 on page 526 of your textbook . &. $essel $essel ele(ents  possibly evolved after the flowers because two basal species  Amborella and  Amborella and Drimys  Drimys lack them. 9ack of vessels was thought to be a primitive characteristic of some basal angiosperms. 7ther features however were inconsistent with the idea that these were primitive plants. The current hypothesis is that Amborella that Amborella is  is primitive 0pi(itively vesselless 1 and never had vessels while others arose after vessels had developed and then lost them. These are referred to as se)on*aily vesselless . 2. Sieve t-.es  probably originated ne)t. everal species still have sieve )ells in their  phloem. 3. All gymnosperms seed ferns and basal angiosperms are or were woo*y plants . The wood of basal angiosperms has many gymnosperms characteristics. Ancestral flowering plants were woody perennial in all probability. probability. :. The he.a)eo-s ha.it  resulted from the loss of vascular cambium and this has occurred in several clades. !. The ann-al ha.it  is a uni6ue angiosperm characteristic. ome groups of angiosperms like grasses bromeliads and o rchids are still changing and evolving. !"ANGING !ON!EPTS A'O%T EARL/ ANGIOSPERMS

C.;. &3! m.y.a.1 m.y.a.1 periods of the eso$oic ;ra. The earliest fossils to be considered those of angiosperms are from the 9ower Cretaceous 0>&3# m.y.a.1. m.y.a.1. They represent both dicot and monocot leaves. These fossils are rare making about 2? of  the plant fossils. 4n the @pper Cretaceous 0ending about ab out ! m.y.a.1 angiosperm fossils are more common outnumbering the fossils of gymnosperms and ferns. @pper Cretaceous and Tertiary Tertiary flora contains fossils that resemble modern genera but are not identical. The oldest angiosperm wood comes the Aptian ;poch of =apan 0>&2! m.y.a.1. %lowers and fruits occurred in the 9ower Cretaceous. !LASSI#I!ATION !LASSI#I!ATION O# #LO&ERING PLANTS

%lowering plants used to be divided into two groups, monocots and dicots. This division has been largely abandoned because of new information that has become beco me available mainly through molecular and cytological studies. 4n general monocots can be recogni$ed by the following traits, 77C7T have floral parts in multiples of three and the seed contains one cotyledon. The endosperm provides the food for the embryo. Benation Benation is usually parallel 0there are e)ceptions1. Their vascular bundles are scattered throughout the ground tissue. The root system is fibrous. +4C7T have floral parts in multiples of four or five and their seeds contain two cotyledons. The cotyledons usually absorb the food from the endosperm first and then  provide the food for the embryo. Benati Benation on is netted. The vascular bundles in the stem

cross5section are arranged in circles 0rings1. They usually have a taproot system for at leas part of their life. Current research supports the hypothesis that monocots are monophyletic and form a single clade. The dicots however appear to be a polyphyletic grouping. ost of the dicots belong to the e-*i)ots0 Three lineages of the remaining dicots form what is called the .asal angiospe(s  because they include what are considered to be the oldest lineages. Another group is called the (agnolii*s . 77C7T have floral parts in multiples of three and the seed contains one cotyledon. The endosperm provides the food for the embryo. Benation Benation is usually parallel 0there are e)ceptions1. Their vascular bundles are scattered throughout the ground tissue. The root system is fibrous. +4C7T have floral parts in multiples of four or five and their seeds contain two cotyledons. The cotyledons usually absorb the food from the endosperm first and then  provide the food for the embryo. Benati Benation on is netted. The vascular bundles in the stem cross5section are arranged in circles 0rings1. They usually have a taproot system for at leas part of their life. Current research supports the hypothesis that monocots are monophyletic and form a single clade. The dicots however appear to be a polyphyletic grouping. ost of the dicots belong to the e-*i)ots0 Three lineages of the remaining dicots form what is called the .asal angiospe(s  because they include what are considered to be the oldest lineages. Another group is called the (agnolii*s .

77C7T have floral parts in multiples of three and the seed contains one cotyledon. The endosperm provides the food for the embryo. Benation Benation is usually parallel 0there are e)ceptions1. Their vascular bundles are scattered throughout the ground tissue. The root system is fibrous. +4C7T have floral parts in multiples of four or five and their seeds contain two cotyledons. The cotyledons usually absorb the food from the endosperm first and then  provide the food for the embryo. Benati Benation on is netted. The vascular bundles in the stem

cross5section are arranged in circles 0rings1. They usually have a taproot system for at leas part of their life. Current research supports the hypothesis that monocots are monophyletic and form a single clade. The dicots however appear to be a polyphyletic grouping. ost of the dicots belong to the e-*i)ots0 Three lineages of the remaining dicots form what is called the .asal angiospe(s  because they include what are considered to be the oldest lineages. Another group is called the (agnolii*s .

 Amborella and  Amborella and Austrobaileyales greatly resemble eudicots* however they cannot be classified as eudicots because the common ancestor that included both of them the eudicots also includes the monocots. See fig.23.9. The same would be the case with the ymphaeales. 'ASAL ANGIOSPERMS