BOTANICAL AND ECOLOGICAL CHARACTERISTICS
SPECIES: Yucca whipplei | Our Lord's Candle 



GENERAL BOTANICAL CHARACTERISTICS : 
Our Lord's candle is a highly variable, rosette-forming, perennial shrub
[23,45].  Subspecies are distinguished by growth form (caespitose or
solitary) and color, size, and shape of leaves and flowers [10,13,17].
The five subspecies also differ in phenological development, fruit set,
and growth habit.  The life history of each subspecies is distinct,
although varying forms do occur in most populations [23].  A correct
determination of the subspecies is important in explaining differences
in regenerative strategies, and variability in plant response to fire,
herbicides, or mechanical disturbance.  Descriptions of the various
subspecies follow:

Subspecies caespitosa:  The stem branches from above the ground to form
a large, crowded clump of numerous, clustered rosettes, with numerous
secondary rosettes forming in the seedling stage.  The plant fruits for
many years, producing several flowerstalks each spring.  Flowerstalks
average 8 feet (2.5 m); leaves are quite rigid and average 2.6 feet (8
dm) in length; flowers are creamy white [18,31,45].

Subspecies intermedia:  This subspecies is similar to ssp. caespitosa in
that it lives for many years and forms a dense clump of rosettes.
However, the clumps are relatively small, and the plant usually only
forms one inflorescence in a season.  After flowering, secondary
rosettes are formed near the base of old flowerstalks, apparently
arising from adventitious axillary buds.  Flowerstalks average 10 feet
(3 m).  Leaves are flat, somewhat more rigid than those of ssp.
caespitosa, and average 3 feet (1 m) long [17,31,45].

Subspecies parishii:  This subspecies grows as a solitary stem and
produces no offshoots; it dies after fruit has formed [13,17,31].  It is
the tallest subspecies of Our Lord's candle, growing from 7 to 21 feet
(2.1-6.4 m) in height [17].  Leaves are flat, flexible, and average 3
feet (1 m) in length [17,31].  After flowering, plants are reduced to a
dried, fibrous base 6 to 8 inches (15-20 cm) across, which often
persists for a number of years [10].

Subspecies percursa:  The stem branches by means of undergound rhizomes
to from large, fairly open clumps made up of distinct rosettes and
rosette clusters [42].  After flowering, the secondary rosettes
sometimes produce adventitious axillary rosettes [17].  Leaves are
shorter than those of other subspecies (approximately 2 feet [4.8 dm])
and quite rigid [18,31].  The stem grows to 1 to 2 feet (3-6 dm) in
height [17,31].  Subspecies percursa flowers and fruits for many years
before the plant reaches maturity [45].  Creamy-white flowers are borne
on a flowerstalk approximately 9 feet (3 m) tall [31].

Subspecies whipplei:  This subspecies is an acaulescent, monocarpic
perennial [1,13,31,42].  The flexible leaves grow 1 to 3 feet (30-80 cm)
in length and form a dense, basal rosette [18,31].  A single, simple
flowerstalk grows to 7 or 8 feet (2-2.5 m) in height [31].  The stem
produces no offshoots [13].  The flowers are white or purple-tinged
[17,31,42].  After flowering, plants are reduced to a resistant fibrous
base, 6 to 8 inches (15-20 cm) across, which often persists for several
years [10].


RAUNKIAER LIFE FORM : 
   Geophyte
   Therophyte


REGENERATION PROCESSES : 
Regeneration in Our Lord's candle varies greatly according to
subspecies.  Subspecies whipplei and parishii are semelparous and
distinguished primarily by size; ssp. caespitosa is an iteroparous
perennial; ssp. percursa has vegetative reproduction; and ssp.
intermedia combines both patterns [23].  Although each subspecies
exhibits a typical mode of reproduction associated with the predominant
growth habit, in most populations some individuals employ different
regenerative strategies.  Many populations have mixtures of monocarpic,
caespitose, and rhizomatous growth forms [23].

Flowering and fruiting:  Attractive, creamy-white or sometimes
purplish-tinged flowers are borne on flowerstalks which generally grow 8
to 10 feet (2.5-3 m) in height (7 to 21 feet [2-6 m] for ssp. parishii)
[45].  The inflorescence is a pedant panicle made up of one hundred to
several thousand flowers [40].  The showy inflorescence of ssp. parishii
is approximately twice as large (averaging 6.5 feet in length and 2 feet
in diameter) as that of ssp. whipplei (averaging 3 feet in length and 13
inches in diameter) [17].  The lower portion of the panicle develops
fruit while the upper part is still flowering [40].  Each dehiscent
fruit contains approximately 150 to 200 flat, smooth, dull black seeds,
which are dispersed by wind [40,45].

Germination:  Seed of ssp. percusa is the heaviest in the taxon and
exhibits the best germination [23], while seed of ssp. parishii is the
lightest and exhibits the poorest germination [23].  Overall germination
of Our Lord's candle is variable, ranging from 0 to 100 percent in
controlled laboratory experiments [4].  When viability is high,
germination may be rapid.  Germination of seed presoaked in water for 24
hours began within 3 days of treatment [42].  Despite the occurrence of
Our Lord's candle in fire-prone chaparral and the importance of sexual
regeneration in most subspecies, seed is vulnerable to high
temperatures.  Significant reductions in germination have been noted
after even brief exposure to high temperatures [18].

Pollination:  One of the most interesting and well-studied aspects of
yucca ecology centers on the symbiotic relationship between yuccas and
their yucca-moth pollinators.  Our Lord's candle relies solely on the
yucca moth (Tegeticula maculata), which consumes a small percentage of
flowers while in the larval stage, for pollination [3].  Seed production
is limited not only by the resources available to the parent plant, but
by pollinator numbers as well [2,14,41].  Many of the regenerative
strategies used by Our Lord's candle reflect competition for potentially
scarce pollinators [40].

Vegetative:  Subspecies caespitosa regenerates vegetatively by producing
multiple, densely packed rosettes from axillary buds early in
development; these rosettes are attached to a small caudex [23].  This
mode of regeneration allows this subspecies to persist or increase even
on harsh sites.  Subspecies caespitosa rarely, if ever, forms rhizomes
[23,45].  Subspecies intermedia regenerates vegetatively via axillary
branching, which occurs only after it is well matured; the base of the
stem and roots persist after flowering to form the subterranean portion
of the new plants [13,17].  Subspecies percusa reproduces vegetatively
through thick, underground rhizomes [13,21,23].  Rhizomes average 2 to 6
feet (0.6-1.8 m) in length, and sprouting often results in the formation
of dense clone [17,23].  


SITE CHARACTERISTICS : 
Although some overlap does occur, each subspecies of Our Lord's candle
occupies its own characteristic habitat:

Subspecies caespitosa grows from 1,800 to 4,000 feet (549-1,219 m) [45]
in areas now dominated by relatively severe continental weather patterns
[18].  This subspecies commonly occurs as an understory species in
California juniper (Juniperus californica) woodlands, and in desert
shrub and chaparral communities [17,31,45].

Subspecies intermedia grows from sea level to 2,000 feet (0-610 m) in
California coastal sage and chaparral [17,31].  It most typically occurs
in areas described as transitional to primarily maritime and continental
influences [18].

Subspecies parishii grows across a broad elevational range occurring
from 1,000 to 8,000 feet (305-2,438 m) [31].  It grows particularly well
on mountain slopes and alluvial fans [31].  This subspecies extends from
chaparral and coastal sage into ponderosa pine (Pinus ponderosa) montane
forests of California [17,31].

Subspecies percursa most commonly occurs on bare, rocky, mountain slopes
or mesas from sea level to 3,608 feet (0-1,100 m) [21,23,45].  It grows
in coastal sage and chaparral communities of southern California
[17,31], environments somewhat more maritime than those occupied by
other subspecies of Our Lord's candle [18].

Subspecies whipplei most commonly grows on dry, stony slopes in
foothills, coastal plains, mountains, and desert fringes of southern
California and Mexico [2,31].  It occurs from 100 to 4,920 feet
(30-1,500 m) [21,31,] in chaparral, coastal sage, and desert shrub
communities [17,31].  This subspecies is now generally found in areas
characterized by a relatively mild, mesic climate [18].

Soils:  All subspecies grow well on a variety of soil types including
unconsolidated or granitic substrates [24].  Growth is most common on
very porous, shallow soils or on rocky outcrops [17].

Plant associates:  Coastal sage - sage (Salvia spp.), lemonade sumac
(Rhus integrifolia), California scrub oak (Quercus dumosa), chokecherry
(Prunus spp.), mountain-mahogany (Cercocarpus betuloides), California
broomsage (Lepidospartum squamatum), and thickleaf yerba-santa
(Eriodycton crassifolium) [24,40].  Desert scrub - creosotebush (Larrea
tridentata).  Chaparral - oaks (Quercus spp.), ceanothus (Ceanothus
spp.), manzanita (Arctostaphylos spp.), chamise (Adenostoma
fasciculatum), and red shank (A. sparsifolium) [40].


SUCCESSIONAL STATUS : 
The successional role of Our Lord's candle has not been well documented.
It probably occurs as a climax species on some fairly harsh sites, and
is well adapted to persist in fire-prone chaparral communities.


SEASONAL DEVELOPMENT : 
Our Lords's candle generally flowers from late February to early June
[1,10].  Only some plants in a particular area flower in any given year,
while the rest undergo vegetative growth.  This annual variation in
reproductive effort may represent an adaptation for greater overall
reproductive success despite limited pollinator availabilty or aberrant
weather patterns.

Flowering:  Individual plants flower for 2 to 7 weeks [1], but the
population flowers for 2 or less commonly 3 months [5,41].  Flowering
tends to be influenced by factors such as rainfall, floral structure,
and elevation [5,10,42].  Flowering generally begins later at higher
elevations, and during extremely dry years, most stands have few if any
individuals which produce flowers [10].  Our Lord's candle may only
bloom for 10 days on very dry sites, while plants on more mesic sites
flower for up to 30 days [40].  Each flower on the inflorescence is only
open for a few days [1].  Flowers at the bottom of the panicle begin
development much earlier than those above [14.]

Fruiting:  Fruit development begins at the bottom of the panicle several
weeks after the first flowers have wilted but while the upper flowers
are still in bloom [42].  Fruit set tends to be low, but is somewhat
higher in fruit at the bottom of the panicle [14].  Fruits reach full
size within a month; seed pods mature, turning dry and gray-brown, by
late summer or fall [40].  The first pods dehisce while the last flowers
are wilting [3].  Wind dispersal usually begins by mid-August [10].

The monocarpic subspecies whipplei and parishii turn brown and die by
late summer or fall in the year of flowering [10].  These plants
generally complete their life cycle within 4 to 7 years [10,28].

Related categories for Species: Yucca whipplei | Our Lord's Candle