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 wouldn’t 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 needn’t 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 Nevada: A. utahensis.

13.                        We have 4 species of Yucca in southern NV: Y. schidigera, Y. baccata, Y. brevifolia, Y. whipplei

14.                         Agaves are CAM plants; some Yuccas are, some not.

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”.