The Families of Flowering Plants Essay

This essay has a total of 1327 words and 7 pages.

The Families of Flowering Plants

Asphodelaceae
(Aloe Family)

CLASSIFICATION
Dahlgren et al. (1985) divided the Monocotyledons into several superorders of which the
Liliiflorae is the largest. The order Asparagales is the largest of the five orders within
Liliiflorea. One of the families within Asparagales recognized by Dahlgren and his
co-workers was Asphodelaceae (Chase et al. (2000). Asphodelaceae consists of the
sub-families, the Asphodeloideae and the Alooideae. The Alooideae consists of six genera
of which Aloe is the largest. The sub-family Alooideae are noted for their spectacular
secondary growth, a characteristic used to define the Alooideae as monophyletic. On the
other hand, some workers within the taxa have considered the above two subfamilies were
for sometime, considered to be separate families, the Asphodelaceae and Alooideae (Dagne
and Yenesaw 1994). Determining the proper phylogeny was difficult because some authors
have argued that Aspodeloideae is not a monophyletic group. Also, the Aspodeloideae are
more varied and share a great deal of morphological similarities between other groups
(Chase et al. 2000). The latest generation of chemical information on species belonging to
these two groups is believed to reveal the relationships among the various taxa and to
assist in establishing taxonomic classifications at various levels (Dagne and Yenesaw
1994). However, there is still not strong enough evidence suggesting both sub-families
should not be included in a single family, the Asphodelaceae (Bisrata 2000).

MORPHOLOGY
Asphodelaceae is a distinct family from other liliod monocot groups by a combination of
several morphological and reproductive features: simultaneous microsporogensis, atypical
ovular structure, lacking steroidal saponins, producing seeds with arils, and the general
presence of anthraquinones. Basic morphological features of genera within the
Asphodelaceae consist of mostly herbs, shrubs, and sometimes arborescent, which grows into
woody forms with trunks that can grow up to several meters high. The leaves are
arrangement is alternate, spiral or 2-ranked that usually form rosettes at base or ends of
the branches. The leaves are often thick and succulent with parallel venation. The
succulent aloes vary in size and morphology from the dwarf rosettes (Adams et al. 2000).
Vascular bundles are arranged in rings around mucilaginous parenchyma tissue, the bundles
have parenchymatous aloin cells in inner bundle sheath near the phloem poles. The
association of aloin cells and central gelatinous zones are synapomorphic for species with
Alooideae (Judd et al. 1999). The perianth is usually bisexual and showy, with 6 distinct
to strongly connate, non-spotted tepals. Reproductive flower parts have 6 distinct stamens
and 3 connate carpels and a superior ovary that contain nectaries in septa. Fruits are
almost always non-fleshy, or fleshy (Lomatophyllum), in a dehiscent loculicidal capsule.
The seeds are either winged, or wingless and contain a dry aril that arises as an annular
invagination at the distal end of the funiculus (Judd et al. 1999; Watson and Dallwitz
1992).

DISTRIBUTION AND DIVERSITY
Asphodelaceae is a large genus containing 15 different genera and 750 species (Judd et al.
1999). Accordingly the genera Aspodeline, Asphodelus, Bulbine, Bulbinella, Eremurus,
Hemiphlacus, Jodrellia, Kniphofia, Paradisea, Simethis and Trachandra are placed in the
sub-family Aspodeloideae while Aloe, Gasteria, Haworthia, Lomatophylum and Poellnitzia are
placed the Alooideae. Most of the species are distributed throughout temperate to tropic
regions of the Old World. The most diverse species are found in arid habitats in Southern
Africa. Only two introduced taxa of Aloe are represented in the continental United States
in parts of southern Florida and California (Judd et al. 1999)

Aloe is the largest genus of 400 species known to occur in a broad range of habitats
mainly in Africa, Madagascar, and Arabia (Viljoen et al. 1998). Aloe is very distinctive
group of plants noted for their often-spectacular secondary growth, which in many areas of
tropical and southern Africa form the dominant plants (Chase et al. 2000).

Aloe is common on rocky hill slopes, often in very large numbers where it creates a
stunning winter display. In the southwestern Africa it grows in grassy fynbos and in
southeastern Africa it may be found on the edges of the karoo. Aloe grows both in the open
and in bushy areas and plants may also differ physically from area to area due to local
conditions (Glenn and Hardy 2000). However, in study done by Britt et al. (2004) in
Madagascar revealed that the rich Aloe diversity in their region has recently been under
threat from habitat destruction.
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