Agavaceae (Century
Plant family)
Monocotyledons
Note:
Agavaceae has often been embedded within the Liliaceae (Lily family), but will be treated here as its
own family.
1. Perennial herbs to arborescent
shrubs, often growing in arid habitats (xerophytes).
2. Leaves - simple,
a.
often spinose-serrate;
b.
alternate and
spirally arranged;
c.
often crowded
into dense rosettes (terminating the stem: agaves)
d.
parallel veined;
e.
typically lanceolate or linear, sessile, stiff (very fibrous) and/or
succulent (Yuccas less succulent than agaves, or non- succulent)
f.
often sharp-pointed at apex.
3. Inflorescence very large terminal, racemose
or paniculate inflorescence
4. Flowers mostly actinomorphic, perfect, hypogynous (superior)
or epigynous (inferior), showy, with sepal nectarines, subtended by conspicuous
bracts.
5. Perianth 6 tepals; petaloid, thick and fleshy; greenish,white or yellow.
6. Androecium 6 stamens, biseriate.
7. Gynoecium - 1 pistil, 3-carpellate, 3-locular
8. Fruit loculicidal capsule (seldom
a berry); seeds flattened with black crust; endosperm copious, very hard.
9. Major genera Agave and Yucca
10.
Economic plants
and products/ Ethnobtanical uses
a.
Tequila and
mescal from fermented sugary sap of certain species of Agave. Mescalero Apaches derive their name from their use of mescal
(or agave) in a number of ways.
b.
Compresses from
the macerated pulp of agaves were used medicinally.
c.
In some species,
the sap can be toxic; in these spp. sap was used as
fish or arrow poison.
d.
Steroidal saponins (active ingredient of oral contraceptives) from
agave and yucca.
e.
Soap form roots
of agave and yucca.
f.
Fiber for rope
and cordage from leaves of Agave (sisal hemp)
g.
Macerated roots
of yuccas were used for the foam in root beer.
h.
The stems of
yucca were (and are) used as a deodorant for livestock.
i.
Young
roots of Joshua-tree was used as
the red elements in Native American basketry.
11.
A
classic case of pollinator-plant interdependency is exemplified by several
Yucca species that are associated with the life cycle of a particular moth
(several species of Tegeticula)
a.
The stigmas of
the Yucca flower are elevated too far above the anthers for self-pollination to
occur; they must be cross-pollinated.
b.
The moth gathers
the putty-like pollen into a ball, then carries the
mass under its head to another flower where it carefully presses the pollen
into the stigmatic tube with its proboscis.
(This
wouldnt occur by chance visitation).
c.
The moth lays one
egg in each ovary locule.
d.
As the larvae and
ovules develop together, a few of the seeds are consumed.
e.
At maturity, the
larvae eat thru the fruit wall and drop to the ground, over-wintering as
cocoons (pupating) and emerging (as moths) when the Yucca is again in bloom.
f.
Risks of tight mutualism: the emergence of adult moths must coincide with
yucca flowering for reproductive needs of both species to be met. If
synchronization of moth emergence with yucca flowering is poor, seed set and
moth reproduction will be low. Yuccas flower sparsely in dry years, and neednt
set seed every year because they flower many times during their long lives.
Yucca moths have a survival strategy analogous to desert annual plants full
grown larvae exit the ripening yucca fruit and burrow into the ground, where
they enter a deep dormancy (diapause). Like many
seeds of annuals, only some of the larvae will metamorphose and emerge as moths
in the following flowering season. The rest remain in diapause
for 2 or more years.
12.
We have one species of Agave in southern
13.
We have 4
species of Yucca in southern NV: Y. schidigera, Y. baccata, Y. brevifolia, Y. whipplei
14.
Agaves are
15.
Reproductive
strategy the periodicity and
intensity of reproduction are intimately related to plant life history and
demography. Some species have a single period of reproductive effort followed
by death, whereas others have repeated periods of low to moderate reproductive
activity.
a.
Plants that produce only once and die are
termed monocarpic
(Gr. One fruit) or semelparous
(Lat. At the same time, birth) Agaves.
b.
Polycarpic (many fruit) or iteroparous (again birth) plants
have repeated periods of reproduction Yuccas
c.
Natural selection
favors those individuals with the greatest fitness i.e. those that make the
greatest proportionate contribution to the future of the population to which
they belong. Life history components affect this contribution, and it does so
thru the media of fecundity and survivorship.
16.
Fibonacci
Series of Numbers a sequence of
numbers named after the Italian mathematician, Leonardo Fibonacci (1170-1250),
in which each number is the sum of the preceeding two
numbers. It is relevant to botany and phyllotaxy in
certain spiral arrangements alternate leaves on a stem; florets in heads of
plants in the sunflower family.
a.
Series of numbers
0,1,1,2,3,5,8,13,21,34,55,89, etc.
b.
Agaves: the angel
between two successively unfolding leaves can be thought of as a fraction of a
circle, a fraction that is the ratio of two Fibonacci numbers.
c.
These two numbers
can be determined by counting leaves around the stem of an agave.
d.
The first number
is the number of spirals or turns around the stem that must be traversed before
a leaf occurs in exactly the same orientation as the starting leaf (one that is
vertically superimposed on top of the starting leaf).
e.
The second number
is the number of leaves that were passed while counting the number of spirals.
f.
Starting with any
agave leaf, 21 leaves must unfold in 8 spirals around the shoot axis before one
points in exactly the same direction as the original
leaf.
g.
The ratio of
these Fibonacci numbers, 8 divided by 21, multiplied by 360 (degrees in a
circle) is 137, the observe angel between successively unfolding leaves of
agave.
h.
Decussate leaves
have 2 leaves per turn of the stem axis.
i.
Many floral parts
conform to the Fibonacci numbers: 3 petals (monocots), 5 petals (many dicots),
13, 21, 34 (number of rays or disk florets of many sunflowers).
j.
So, if you are
aware of how the rays of a daisy (Asteraceae) conform to Fibonacci numbers, you
may be able to pre-determine the outcome of your she loves me, she loves me
not.