The
flowering plants or
angiosperms (
Angiospermae or
Magnoliophyta) are the most diverse group of
land plants. The flowering plants and
the
gymnosperms are the only extant
groups of
seed plants. The flowering
plants are distinguished from other seed
plants by a series of
apomorphies, or derived
characteristics.
The ancestors of flowering plants diverged from
gymnosperms around 245–202 million years ago,
and the first flowering plants known to exist are from 140 million
years ago. They have become widespread around 100 million years
ago, but replaced
conifers as the dominant
trees only around 60-70 million years ago.
Angiosperm derived characteristics
The flowers, which are the
reproductive organs of flowering plants,
are the most remarkable feature distinguishing them from other seed
plants. Flowers aid angiosperms by enabling a wider range of
adaptability and broadening the
ecological niches open to them. This has
allowed flowering plants to largely dominate
terrestrial ecosystems.
- Stamens with two pairs of pollen
sacs
Stamens are much lighter than the corresponding organs of
gymnosperms and have contributed to the diversification of
angiosperms through time with
adaptations
to specialized
pollination syndromes,
such as particular pollinators. Stamens have also become modified
through time to prevent
self-fertilization, which has permitted
further diversification, allowing angiosperms eventually to fill
more niches.
- Reduced male parts, three cells
The male
gametophyte in angiosperms is
significantly reduced in size compared to those of gymnosperm seed
plants. The smaller pollen decreases the time from pollination —
the pollen grain reaching the female plant — to
fertilization of the ovary; in gymnosperms
fertilization can occur up to a year after pollination, while in
angiosperms the fertilization begins very soon after pollination.
The shorter time leads to angiosperm plants setting seeds sooner
and faster than gymnosperms, which is a distinct evolutionary
advantage.
- Closed carpel enclosing the ovules
(carpel or carpels and accessory parts may become the fruit)
The closed carpel of angiosperms also allows adaptations to
specialized pollination syndromes and controls. This helps to
prevent self-fertilization, thereby maintaining increased
diversity. Once the ovary is fertilized, the carpel and some
surrounding tissues develop into a fruit. This fruit often serves
as an attractant to seed-dispersing animals. The resulting
cooperative relationship presents another advantage to angiosperms
in the process of
dispersal.
- Reduced female gametophyte, seven cells with eight nuclei
The reduced female gametophyte, like the reduced male gametophyte,
may be an adaptation allowing for more rapid seed set, eventually
leading to such flowering plant adaptations as annual herbaceous
life cycles, allowing the flowering plants to fill even more
niches.
Endosperm formation generally begins after fertilization and before
the first division of the
zygote. Endosperm
is a highly nutritive tissue that can provide food for the
developing
embryo, the cotyledons, and
sometimes for the
seedling when it first
appears.
These distinguishing characteristics taken together have made the
angiosperms the most diverse and numerous land plants and the most
commercially important group to humans. The major exception to the
dominance of terrestrial ecosystems by flowering plants is the
coniferous forest.
Evolution
Land plants have existed for about 425 million years. Early land
plants
reproduced sexually with
flagellated, swimming sperm, like the green algae from which they
evolved. An adaptation to terrestrialization was the development of
upright meiosporangia for dispersal by
spores
to new habitats. This feature is lacking in the descendants of
their nearest algal relatives, the Charophycean green algae. A
later terrestrial adaptation took place with retention of the
delicate, avascular sexual stage, the gametophyte, within the
tissues of the vascular sporophyte. This occurred by spore
germination within sporangia rather than spore release, as in
non-seed plants. A current example of how this might have happened
can be seen in the precocious spore germination in Sellaginella,
the spike-moss. The result for the ancestors of angiosperms was
enclosing them in a case, the
seed. The first
seed bearing plants, like the
ginkgo, and
conifers (such as
pines
and
firs), did not produce flowers.
Interestingly, the pollen grains (males) of Ginkgo and cycads
produce a pair of flagellated, mobile sperm cells that "swim" down
the developing pollen tube to the female and her eggs.
The apparently sudden appearance of relatively modern flowers in
the fossil record posed such a problem for the theory of
evolution that it was called an "abominable
mystery" by
Charles Darwin. However,
the fossil record has grown since the time of Darwin, and recently
discovered angiosperm fossils such as
Archaefructus, along
with further discoveries of fossil gymnosperms, suggest how
angiosperm characteristics may have been acquired in a series of
steps. Several groups of extinct gymnosperms, particularly
seed ferns, have been proposed as the
ancestors of flowering plants
but there is no continuous fossil evidence showing exactly how
flowers evolved. Some older fossils, such as the upper
Triassic Sanmiguelia, have been suggested. Based on
current evidence, some propose that the ancestors of the
angiosperms diverged from an unknown group of gymnosperms during
the late
Triassic (245–202 million years
ago). A close relationship between angiosperms and
gnetophytes, proposed on the basis of
morphological evidence, has more
recently been disputed on the basis of
molecular evidence that suggest
gnetophytes are instead more closely related to other
gymnosperms.
The earliest known angiosperm
macrofossil,
Archaefructus liaoningensis, is dated to
about 125 million years BP (the
Cretaceous period), while pollen considered to be
of angiosperm origin takes the
fossil record
back to about 130 million years BP. There is, however,
circumstantial chemical evidence for the existence of angiosperms
as early as 250 million years ago.
Oleanane, a
secondary metabolite produced by many
flowering plants, has been found in
Permian
deposits of that age together with fossils of
gigantopterids. Gigantopterids are a group of
extinct seed plants that share many morphological traits with
flowering plants, although they are not known to have been
flowering plants themselves.
Recent
DNA analysis (molecular systematics) show that
Amborella trichopoda, found on
the Pacific island of New Caledonia
, belongs to a sister
group of the other flowering plants, and morphological studies
suggest that it has features that may have been characteristic of
the earliest flowering plants.
The great angiosperm
radiation,
when a great diversity of angiosperms appears in the fossil record,
occurred in the mid-
Cretaceous
(approximately 100 million years ago). However, a study in 2007
estimated that the division of the five most recent (the genus
Ceratophyllum, the family
Chloranthaceae, the
eudicots, the
magnoliids,
and the
monocots) of the eight main groups
occurred around 140 million years ago.By the late Cretaceous,
angiosperms appear to have dominated environments formerly occupied
by
ferns and
cycadophytes, but large canopy-forming trees
replaced
conifers as the dominant trees only
close to the end of the
Cretaceous 65
millions years ago or even later, at the beginning of the
Tertiary. The radiation of herbaceous angiosperm
occurred much later. Yet, many fossil plants recognizable as
belonging to modern families (including
beech,
oak,
maple, and
magnolia) appeared already at late
Cretaceous.
It is generally assumed that the
function of flowers, from the start, was
to involve mobile
animals in their
reproduction processes. That is, pollen can be
scattered even if the flower is not brightly
colored or oddly shaped in a way that attracts
animals; however, by expending the energy required to create such
traits, angiosperms can enlist the aid of animals and thus
reproduce more efficiently.
Island genetics provides one
proposed explanation for the sudden, fully developed appearance of
flowering plants. Island genetics is believed to be a common source
of
speciation in general, especially when
it comes to radical adaptations that seem to have required inferior
transitional forms. Flowering plants may have evolved in an
isolated setting like an
island or island
chain, where the plants bearing them were able to develop a highly
specialized relationship with some specific animal (a
wasp, for example). Such a relationship, with a
hypothetical wasp carrying pollen from one plant to another much
the way
fig wasps do today, could result in
both the plant(s) and their partners developing a high degree of
specialization. Note that
the wasp example is not incidental;
bees, which
apparently evolved specifically due to mutualistic plant
relationships, are descended from wasps.
Animals are also involved in the distribution of seeds.
Fruit, which is formed by the enlargement of flower
parts, is frequently a seed-dispersal tool that attracts animals to
eat or otherwise disturb it, incidentally scattering the seeds it
contains (see
frugivory). While many such
mutualistic relationship remain too
fragile to survive
competition
and spread widely, flowering proved to be an unusually effective
means of reproduction, spreading (whatever its origin) to become
the dominant form of land plant life.
Flower
ontogeny uses a combination of
genes normally responsible for forming new
shoots. The most primitive flowers are thought to have had a
variable number of flower parts, often separate from (but in
contact with) each other. The flowers would have tended to grow in
a spiral pattern, to be bisexual (in plants, this means both male
and female parts on the same flower), and to be dominated by the
ovary (female part). As flowers grew
more advanced, some variations developed parts fused together, with
a much more specific number and design, and with either specific
sexes per flower or plant, or at least "ovary inferior".
Flower evolution continues to the present day; modern flowers have
been so profoundly influenced by humans that some of them cannot be
pollinated in nature. Many modern, domesticated flowers used to be
simple weeds, which only sprouted when the ground was disturbed.
Some of them tended to grow with human crops, perhaps already
having symbiotic
companion plant
relationships with them, and the prettiest did not get plucked
because of their beauty, developing a dependence upon and special
adaptation to human affection.
Classification
|
The current phylogeny of the
flowering plants. |
There are eight groups of living angiosperms:
- Amborella —
a single species of shrub from New Caledonia

- Nymphaeales — about 80 species —
water lilies and Hydatellaceae
- Austrobaileyales — about 100
species of woody plants from various
parts of the world
- Chloranthales — several dozen
species of aromatic plants with toothed leaves
- Ceratophyllum — about 6
species of aquatic plants, perhaps
most familiar as aquarium plants
- magnoliids — about 9,000 species,
characterized by trimerous flowers, pollen
with one pore, and usually branching-veined leaves — for example
magnolias, bay
laurel, and black pepper
- eudicots — about 175,000 species,
characterized by 4- or 5- merous flowers,
pollen with three pores, and usually branching-veined leaves — for
example sunflowers, petunia, buttercup,
apples and oaks
- monocots — about 70,000 species,
characterized by trimerous flowers, a single cotyledon, pollen with one pore, and usually
parallel-veined leaves — for example grass,
orchids, and palm
The exact relationship between these eight groups is not yet clear,
although it has been determined that the first three groups to
diverge from the ancestral angiosperm were
Amborellales,
Nymphaeales, and
Austrobaileyales. The term
basal angiosperms refers to these three
groups.
History of classification

From 1736, an illustration of Linnaean
classification.
The botanical term "Angiosperm", from the
Ancient Greek αγγείον,
angeíon
(receptacle, vessel) and σπέρμα, (seed), was coined in the form
Angiospermae by
Paul Hermann in 1690,
as the name of that one of his primary divisions of the plant
kingdom. This included flowering
plants possessing seeds enclosed in capsules, distinguished from
his Gymnospermae, or flowering plants with
achenial or schizo-carpic fruits, the whole fruit or
each of its pieces being here regarded as a seed and naked. The
term and its antonym were maintained by
Carolus Linnaeus with the same sense, but
with restricted application, in the names of the orders of his
class
Didynamia. Its use with any approach
to its modern scope only became possible after 1827, when
Robert Brown established the
existence of truly naked ovules in the
Cycadeae and
Coniferae,
and applied to them the name Gymnosperms. From that time onwards,
so long as these Gymnosperms were, as was usual, reckoned as
dicotyledonous flowering plants, the term Angiosperm was used
antithetically by botanical writers, with varying scope, as a
group-name for other dicotyledonous plants.
In 1851,
Hofmeister discovered
the changes occurring in the embryo-sac of flowering plants, and
determined the correct relationships of these to the
Cryptogamia. This fixed the position of
Gymnosperms as a class distinct from Dicotyledons, and the term
Angiosperm then gradually came to be accepted as the suitable
designation for the whole of the flowering plants other than
Gymnosperms, including the classes of Dicotyledons and
Monocotyledons. This is the sense in which the term is used
today.
In most taxonomies, the flowering plants are treated as a coherent
group. The most popular descriptive name has been Angiospermae
(Angiosperms), with Anthophyta ("flowering plants") a second
choice. These names are not linked to any rank. The
Wettstein system and the
Engler system use the name Angiospermae, at
the assigned rank of subdivision. The
Reveal system treated flowering plants as
subdivision
Magnoliophytina (Frohne
& U. Jensen ex Reveal, Phytologia 79: 70 1996), but later split
it to Magnoliopsida, Liliopsida and Rosopsida. The
Takhtajan system and
Cronquist system treat this group at the
rank of
division, leading to the
name Magnoliophyta (from the family name Magnoliaceae). The
Dahlgren system and
Thorne system treat this group at the
rank of class, leading to the name Magnoliopsida. However, the
APG system, of 1998, and the
APG II system, of 2003, do not treat it as a
formal taxon but rather treat it as a clade without a formal
botanical name and use the name
angiosperms for this clade.
The internal classification of this group has undergone
considerable revision. The
Cronquist
system, proposed by
Arthur
Cronquist in 1968 and published in its full form in 1981, is
still widely used, but is no longer believed to accurately reflect
phylogeny. A general consensus about how
the flowering plants should be arranged has recently begun to
emerge, through the work of the
Angiosperm Phylogeny Group, who
published an influential reclassification of the angiosperms in
1998. An update incorporating more recent research was published as
APG II in 2003.
Traditionally, the flowering plants are divided into two groups,
which in the Cronquist system are called
Magnoliopsida (at
the rank of class, formed from the family name
Magnoliacae) and
Liliopsida (at the rank of
class, formed from the family name
Liliaceae). Other descriptive names allowed
by Article 16 of the
ICBN include
Dicotyledones or
Dicotyledoneae,
and
Monocotyledones or
Monocotyledoneae, which have a long history of use. In
English a member of either group may be called a
dicotyledon (plural
dicotyledons)
and
monocotyledon (plural
monocotyledons), or abbreviated, as
dicot (plural
dicots) and
monocot (plural
monocots).
These names derive from the observation that the dicots most often
have two
cotyledons, or embryonic
leaves, within each seed. The monocots usually have only one, but
the rule is not absolute either way. From a diagnostic point of
view the number of cotyledons is neither a particularly handy nor
reliable character.
Recent studies, as by the APG, show that the monocots form
holophyletic or
monophyletic group; this
clade is given the name
monocots. However, the dicots are not (they
are a
paraphyletic group).
Nevertheless, within the dicots a monophyletic group does exist,
called the
eudicots or
tricolpates, and including most
of the dicots. The name
tricolpates derives from a type of
pollen found widely within this group. The
name
eudicots is formed combining
dicot with the
prefix
eu- (from Greek, for "well," or "good," botanically
indicating "true"), as the eudicots share the characters
traditionally attributed to the dicots, such as flowers with four
or five parts (four or five
petals, four or
five
sepals). Separating this group of
eudicots from the rest of the (former) dicots leaves a remainder,
which sometimes are called informally
palaeodicots (Greek prefix
"palaeo-" means "old"). As this remnant group is not
monophyletic this is a term of convenience only.
Flowering plant diversity

Various flower colors and shapes
The number of
species of flowering plants is
estimated to be in the range of 250,000 to 400,000.
The number of
families in APG
(1998) was 462. In APG II (2003) it is not settled; at maximum it
is 457, but within this number there are 55 optional segregates, so
that the minimum number of families in this system is 402.
The diversity of flowering plants is not evenly distributed. Nearly
all species belong to the eudicot (75%), monocot (23%) and
magnoliid (2%) clades. The remaining 5 clades contain a little over
250 species in total, i.e., less than 0.1% of flowering plant
diversity, divided among 9 families.
The most diverse families of flowering plants, in their APG
circumscriptions, in order of number of species, are:
- Asteraceae or Compositae (daisy
family): 23,600 species
- Orchidaceae (orchid family): 21,950 species
- Fabaceae or Leguminosae (pea family): 19,400
- Rubiaceae (madder family): 13,183
- Poaceae or Gramineae (grass family): 10,035
- Lamiaceae or Labiatae (mint family): 7,173
- Euphorbiaceae (spurge family): 5,735
- Myrtaceae (myrtle family): 4,620
- Melastomataceae (melastome family): 4,570
- Cyperaceae (sedge family): 4,350
In the list above (showing only the 10 largest families), the
Orchidaceae, Poaceae, and Cyperaceae are monocot families; the
others are eudicot families.
Vascular anatomy
[[Image:Stem-histology-cross-section-tag.svg|thumb|right|250px|Cross-section
of a stem of the angiosperm
flax:
1.
Pith,
2.
Protoxylem,
3.
Xylem I,
4.
Phloem I,
5.
Sclerenchyma (
bast fibre),
6.
Cortex,
7.
Epidermis]]
The amount and
complexity of
tissue-formation in flowering plants exceeds that of Gymnosperms.
The
vascular bundles of the stem are
arranged such that the
xylem and
phloem form concentric rings.
In the Dicotyledons, the bundles in the very young stem are
arranged in an open ring, separating a central pith from an outer
cortex. In each bundle, separating the xylem and phloem, is a layer
of
meristem or active formative tissue
known as
cambium. By the formation of a
layer of cambium between the bundles (interfascicular cambium) a
complete ring is formed, and a regular periodical increase in
thickness results from the development of xylem on the inside and
phloem on the outside. The soft phloem becomes crushed, but the
hard wood persists and forms the bulk of the stem and branches of
the woody perennial. Owing to differences in the character of the
elements produced at the beginning and end of the season, the wood
is marked out in transverse section into concentric rings, one for
each
season of growth, called
annual rings.
Among the Monocotyledons, the bundles are more numerous in the
young stem and are scattered through the ground tissue. They
contain no cambium and once formed the stem increases in diameter
only in exceptional cases.
The flower, fruit, and seed
Flowers

A collection of flowers forming an
inflorescence.
The characteristic feature of angiosperms is the flower. Flowers
show remarkable variation in form and elaboration, and provide the
most trustworthy external characteristics for establishing
relationships among angiosperm species. The function of the flower
is to ensure fertilization of the ovule and development of
fruit containing
seeds. The floral
apparatus may arise terminally on a shoot or from the axil of a
leaf (where the
petiole attaches to
the stem). Occasionally, as in
violets, a flower arises singly in the axil
of an ordinary foliage-leaf. More typically, the flower-bearing
portion of the plant is sharply distinguished from the
foliage-bearing or vegetative portion, and forms a more or less
elaborate branch-system called an
inflorescence.
The reproductive cells produced by flowers are of two kinds.
Microspores, which will divide to become
pollen
grains, are the "male" cells and are borne in the
stamens (or microsporophylls). The "female" cells
called megaspores, which will divide to become the egg-cell
(
megagametogenesis), are contained
in the
ovule and enclosed in the
carpel (or megasporophyll).
The flower may consist only of these parts, as in
willow, where each flower comprises only a few
stamens or two carpels. Usually other structures are present and
serve to protect the sporophylls and to form an envelope attractive
to pollinators. The individual members of these surrounding
structures are known as
sepals and
petals (or
tepals in flowers such
as
Magnolia where sepals and
petals are not distinguishable from each other). The outer series
(calyx of sepals) is usually green and leaf-like, and functions to
protect the rest of the flower, especially the bud. The inner
series (corolla of petals) is generally white or brightly colored,
and is more delicate in structure. It functions to attract
insect or
bird pollinators.
Attraction is effected by color,
scent, and
nectar, which may be secreted in some part of
the flower. The characteristics that attract pollinators account
for the popularity of flowers and flowering plants among
humans.
While the majority of flowers are perfect or
hermaphrodite (having both male and female
parts in the same flower structure), flowering plants have
developed numerous morphological and
physiological mechanisms to reduce or prevent
self-fertilization. Heteromorphic flowers have short carpels and
long stamens, or vice versa, so animal
pollinators cannot easily transfer pollen to the
pistil (receptive part of the carpel). Homomorphic flowers may
employ a biochemical (physiological) mechanism called
self-incompatibility to
discriminate between self- and non-self pollen grains. In other
species, the male and female parts are morphologically separated,
developing on different flowers.
Fertilization and embryogenesis

angiosperm life cycle
Double fertilization refers to
a process in which two
sperm cells fertilize
cells in the
ovary. This process begins when a
pollen grain adheres to the stigma of the
pistil (female reproductive structure), germinates,
and grows a long
pollen tube. While this
pollen tube is growing, a haploid generative cell travels down the
tube behind the tube nucleus. The generative cell divides by
mitosis to produce two haploid (
n) sperm cells. As the
pollen tube grows, it makes its way from the stigma, down the style
and into the ovary. Here the pollen tube reaches the micropyle of
the ovule and digests its way into one of the synergids, releasing
its contents (which include the sperm cells). The synergid that the
cells were released into degenerates and one sperm makes its way to
fertilize the egg cell, producing a diploid (2
n) zygote.
The second sperm cell fuses with both central cell nuclei,
producing a triploid (3
n) cell. As the zygote develops
into an embryo, the triploid cell develops into the endosperm,
which serves as the embryo's food supply. The ovary now will
develop into fruit and the ovule will develop into seed.
Fruit and seed
As the development of embryo and endosperm proceeds within the
embryo-sac, the sac wall enlarges and combines with the
nucellus (which is likewise enlarging) and the
integument to form the
seed-coat. The ovary wall develops to form the
fruit or
pericarp, whose form
is closely associated with the manner of distribution of the
seed.
Frequently the influence of fertilization is felt beyond the
ovary, and other parts of the flower take part
in the formation of the fruit,
e.g. the floral receptacle
in the
apple,
strawberry and others.
The character of the seed-coat bears a definite relation to that of
the fruit. They protect the embryo and aid in dissemination; they
may also directly promote germination. Among plants with
indehiscent fruits, the fruit generally provides protection for the
embryo and secures dissemination. In this case, the seed-coat is
only slightly developed. If the fruit is
dehiscent and the seed is exposed, the
seed-coat is generally well developed, and must discharge the
functions otherwise executed by the fruit.
Economic importance
Agriculture is almost entirely dependent
on angiosperms, either directly or indirectly through
livestock feed. Of all the families plants, the
Poaceae, or grass family, is by far the most
important, providing the bulk of all feedstocks (
rice, corn —
maize,
wheat,
barley,
rye,
oats,
pearl millet,
sugar
cane,
sorghum). The
Fabaceae, or legume family, comes in second place.
Also of high importance are the
Solanaceae, or nightshade family (
potatoes,
tomatoes, and
pepper, among others), the
Cucurbitaceae, or
gourd
family (also including
pumpkins and
melons), the
Brassicaceae,
or
mustard plant family (including
rapeseed and
cabbage), and the
Apiaceae,
or
parsley family. Many of our fruits come
from the
Rutaceae, or rue family, and the
Rosaceae, or rose family (including
apples,
pears,
cherries,
apricots,
plums, etc.).
In some parts of the world, certain single species assume paramount
importance because of their variety of uses, for example the
coconut (
Cocos nucifera) on Pacific
atolls, and the olive (
Olea europaea) in the
Mediterranean region.
Flowering plants also provide economic resources in the form of
wood,
paper, fiber
(
cotton,
flax, and
hemp, among others), medicines (
digitalis,
camphor),
decorative and landscaping plants, and many other uses. The main
area in which they are surpassed by other plants is
timber production.
See also
References
- Darwin's abominable mystery: Insights from a
supertree of the angiosperms. Proceedings of the National
Academy of Sciences of the United States of America. T. Jonathan
Davies, Timothy G. Barraclough, Mark W. Chase, Pamela S. Soltis,
Douglas E. Soltis, and Vincent Savolainen. Published (online)
February 6, 2004.
- NOVA — First Flower — Flowers Modern and
Ancient — PBS
- Oily Fossils Provide Clues To The Evolution Of
Flowers — ScienceDaily (Apr. 5, 2001)
- NOVA — Transcripts — First Flower — PBS Airdate: April
17, 2007
- Amborella not a "basal angiosperm"? Not so fast
-- Soltis and Soltis 91 (6): 997 -- American Journal of Botany
- South Pacific plant may be missing link in
evolution of flowering plants — Public release date:
17-May-2006
- Using plastid genome-scale data to resolve
enigmatic relationships among basal angiosperms- Communicated
by David L. Dilcher, University of Florida, Gainesville, FL, August
28, 2007 (received for review June 15, 2007) — PNAS
- Wilson Nichols Stewart & Gar W. Rothwell,
Paleobotany and the evolution of plants, 2nd ed.,
Cambridge Univ. Press 1993, p. 498
- Age-Old Question On Evolution Of Flowers Answered —
15-Jun-2001
- Human Affection Altered Evolution of Flowers —
By Robert Roy Britt, LiveScience Senior Writer (posted: 26 May 2005
06:53 am ET)
- >
External links
- Cronquist, Arthur. (1981) An Integrated System of
Classification of Flowering Plants. Columbia Univ. Press, New
York.
- Dilcher, D. 2000. Toward a new synthesis: Major evolutionary
trends in the angiosperm fossil record. PNAS [Proceedings of
the National Academy of Sciences of the United States of
America] 97: 7030-7036 (available online here)
- Oldest Known Flowering Plants Identified By
Genes, William J. Cromie, Harvard Gazette, December 16, 1999.
- L. Watson and M.J. Dallwitz (1992 onwards). The families of flowering plants: descriptions,
illustrations, identification, information retrieval.
- Simpson, M.G. Plant Systematics. Elsevier Academic
Press. 2006.
- Raven, P.H., R.F. Evert, S.E. Eichhorn. Biology of
Plants, 7th Edition. W.H. Freeman. 2004.