Carnivorous Plants Website
Carnivorous Plants in the Wilderness
by Makoto Honda
 

  

  Preface

  Contents

  Introduction

  1.
Pitcher Plants
  2.
Cobra Plant
  3.
Sundews
  4.
Venus Flytrap
  5.
Butterworts
  6.
Bladderworts

  References

 

 

 

  HOME

 

Cobra Plant    Darlingtonia             PHOTOGRAPHY
Last update: December 11, 2004

General

The plant was discovered in 1841 by William D. Brackenridge, assistant botanist of the U.S. Exploring Expedition, in a marsh a few miles south of Mt. Shasta in northern California. John Torrey, a distinguished botanist of the 19th century, recognized a close relationship to the eastern pitcher plants yet a clear difference in floral characteristics, and established a new genus in the pitcher plant family, naming it
Darlingtonia californica, in honor of his friend and botanist, William Darlington.*  The genus Darlingtonia is monotypic, i.e. only one species in the genus. The pitcher plant family Sarraceniaceae contains two other genera, Sarracenia (Eastern pitcher plants) and Heliamphora (South American pitcher plants).**

The cobra plant is a herbaceous perennial consisting of a rhizome, with fibrous roots. Tubular pitcher leaves arise directly from the rhizome, forming a rosette. In this species, the hood of the pitcher is well developed to form a dome, with the pitcher opening facing downward. The pitcher lid is modified into a two-lobed, fishtail-like appendage projecting downward from the front edge of the opening. A peculiar feature of the plant is that the leaves twist about 180 degrees as they grow. As a result, the pitcher openings tend to face outwardly from the plant center. This conceivably provides wider coverage for prey acquisition. The direction of the twist seems to be just about even between clockwise and counter-clockwise in nature, though within a given individual the direction is fixed.***

In a typical natural habitat, a mature pitcher leaf stands between 40-60cm tall. Leaves reaching 100cm are found in some low-light conditions. Seen in the field, the overhanging hood of the pitcher leaf gives an impression of a deadly cobra about to strike in imminent defense, hence the common name.  Other names for the plant include "cobra lily" and "California pitcher plant".

The distribution of cobra plants is limited to northern California and the adjacent southwestern part of Oregon, where the colonies are highly localized in characteristic marshy habitats often with fresh, running waters. 

Habitat

Leaves of the cobra plant sprouting out in the thousands on grass-covered slopes in the mountain habitat -- with their cobra heads glowing in a golden hue -- offer a truly spectacular sight in nature.

Streams flowing through mountain meadow present an ideal habitat for this remarkable species of the pitcher plant family. Cold waters from the mountain springs rush through a mild mountain slope in a sparsely populated coniferous forest, forming a wide band of marshy surface along the water path. It is in such an exacting setup that the colonies of the cobra plants thrive. The plants' fondness for this particular setup is clearly manifested in the astonishing similarity of many a montane habitat throughout their range.

Many cobra plant sites are also known to be located on or near serpentine rocks, providing continuous stream flowing through serpentine rock formations in the region. The soils in these habitats are acid and poor in nutrition, in general conformity with other carnivorous plant habitats. Toxicity of the soil.... 

Many populations are found in the montane habitats at an altitude of up to 2500m, although some vigorous stands of cobra plants can be seen almost at the sea level along the Oregon coast (south of the city of Florence). The plants seem to be tolerant to this climatic variation (Juniper, et al. 1989).

As for accompanying carnivorous plants, cobra plants are often found with Drosera rotundifolia (round-leaf sundew) at the southern end of its range (Rondeau 1995).  In southern Oregon, there are some colonies where Pinguicula macroceras ssp. nortensis (butterwort) grows extensively alongside Darlingtonia

Rondeau (1995) recognizes two kinds of primary habitats for Darlingtonia: A typical montane habitat is what is duly described as a seep, often with a moderate slope, having constant water flow on the soil surface. The plants also grow in what can be described as "Darlingtonia bogs", which are only found along the coastal plains in Oregon, with near-zero slope, but with external water input and drainage (Rondeau 1995).     

In summer, the daytime temperature may reach 35 degrees Celsius in some localities. However, the running water where the root is submerged rarely exceeds mid-20 degrees Celsius on the same day. This constant supply of cold water from mountain springs seems essential for the healthy and vigorous growth of the cobra plant. The plants are rarely seen in standing water in nature. Because of this extreme intolerance to high temperature at the root, the cobra plant is not a very easy plant to maintain in cultivation. Even if you live within the perimeter of the cobra plant's natural distribution in Oregon and California, it is unlikely that you would have great success with growing cobra plants if you just leave them in a water-filled tray; you need to drop an ice cube or two on the pot everyday during the hot summer days!  

On the other hand, in the inland localities of northern California and adjacent Oregon, cobra plants endure extremes of low temperature during the winter months, sometimes covered with frost, ice, and snow!

There is some debate as to which direction the cobra plant colonies face. From field observations, it is easy to see that Darlingtonia enjoys plenty of sunlight. Plants growing in a sunny location assume a colorful tint on the domed hood toward the orifice and the fishtail appendage -- a definite advantage in attracting prey, that is absent in all-green, shade-grown plants, in nature or in cultivation. Many major colonies face south-east. Rondeau (1995) attributes this to local hydrology of the region more than anything else.  There are many fine colonies in the mountain meadow whose slope is so slight that it is rather academic to speak of colony orientation (in relation to the amount of sunlight the plants receive). And there are some colonies facing north. We also find large colonies that are over-grown by shrubberies and conifers, with rather limited sunlight, regardless of their orientation. Darlingtonia seems to persist well in those low-light conditions as long as there is plenty of water supply, though the long-term health of such colonies is uncertain.

Rebecca M. Austin

Throughout the recorded history of Darlingtonia, Rebecca Austin was the first to study the plants in detail and make pioneering field work. (Juniper, et al. 1989)  Moving to northern California with her husband and their three young children, Rebecca Austin was fascinated by this unique Californian pitcher plant. Living near great cobra plant sites, including Butterfly Valley (now a protected nature preserve), she spent many days observing the plants in the field, sometimes carrying her sewing to the colony, even putting out a tent for overnight observations. She also pursued her observation in the midst of a violent thunderstorm, convincing herself that the rainwater did not enter the pitcher. From 1875 to 1877, she diligently communicated her detailed field observations to W. M. Canby, a botanist in the East. Canby sent stationery to help her work and encouraged her observations. The then-newly-published book "insectivorous plants" by Charles Darwin was sent to her to aid her studies. 

Trap Structure and Attraction 

The domed pitcher looks light yellow-green on the hood and gets darker green toward the base. The area along the pitcher opening through the fishtail appendage assumes a reddish coloration in plants growing in the sun.

The basic trap structure of the pitcher leaf is similar to that of the eastern pitcher plants. Together with the attractive colors of the leaf, prey is lured to the trap by nectar-secreting glands scattered over much of the pitcher exterior.

The forked, fishtail appendage has numerous nectar glands. Its surface is covered with short, stiff hairs, pointing toward the pitcher opening. For a flying insect, the fishtail appendage provides a convenient landing site, as well as a feeding ground.  Further toward the domed hood, the insect finds more nectar around the pitcher opening. The leaf edge of the orifice rolls inwards, forming the “nectar roll” around the pitcher opening. This is  where the nectar production is most abundant.  

The hooded dome interior is covered with fine hairs. The dome and the upper part of the pitcher are scattered with many areoles, called fenestrations. These patches are completely void of chlorophyll and other pigments, forming truly translucent windows. Seen against a blue sky, the brightly lit ceiling of the dome encourages the insect, already enjoying nectar on the fishtail appendage, to venture into the dome interior. 

Once inside the dome, the rolled-up inner margin of the pitcher opening somewhat conceals the true exit from insect's view, and the light windows provide the illusion of false exits. The insect, instinctively seeking an exit in the direction of light, often slams against the dome ceiling in its attempt to fly through, and tumbles down into the spiral depth of the cobra leaf.

Right below the dome interior extends a hairless, detachable waxy zone which offers an extremely poor footing for the insect. Further down along the pitcher, as the tube gets narrower, there grow long, intermeshing, down-pointing hairs designed to prevent insect's ascent. This retention zone continues almost to the end of the pitcher. At the very bottom lies a short, smooth zone where there is no glands.

A younger pitcher leaf tends to assume a more tilted angle, with the forked appendage often touching the ground. In this posture, the appendage serves as a ladder leading to the pitcher opening for crawling insects, such as ants.

In the field, at the end of the summer season, pitchers are often seen half-filled with exoskeletal remains of insect bodies, attesting to the trapping efficacy of the pitcher leaves.

Digestion and Absorption

The cobra plant normally retains small amount of liquid at the bottom of the pitcher. Unlike the eastern pitcher plants, the well-developed domed hood structure of the leaf all but precludes the possibility of rainwater entering the pitcher. In Darlingtonia, an unopened pitcher retains some liquid. Studies have shown that a certain chemical stimulation (like beef broth) precipitates a large amount of fluid secretions into the pitcher. The insect prey falling in the pitcher equally causes the fluid level to rise. This reaction to the chemical stimulation is also seen in some eastern pitcher plants.

Unlike most species of the eastern pitcher plants, however, the cobra plant does not possess any digestive glands in the pitcher interior and no enzyme secretions has been detected. The digestion of prey is carried out solely with the aid of external bacteria.

"In Darlingtonia", Juniper et al. note, "which we consider to be a relatively primitive carnivore in some respect, there are nectar glands, but the glands of the digestive zone do not appear to secrete enzymes. Thus, nectar secretionsmay have developed before enzyme secretions in a species which relies on a larval-protozon-bacterial chain breakdown for digestion of prey. Presumably this dependency could have been the integral feature in the development of present-day highly adapted species." Juniper et al. also note, "...nectar secretionsmay more readily develop than enzyme secretions because it was probably based initially on the exudation of phloem contents already present, needing only to become more concentrated. A mechanism was already present in floral nectaries."

The bottom part of the pitcher, where the liquid is usually retained and where the digestion takes place, does not possess any special glands. The permeability of the inner wall due to cuticle discontinuity allows the absorption of digestive material into the leaf tissue.

In the pitcher fluid, many white worms are often found, apparently feeding on the captured prey. This observation was first made by Rebecca Austin. She described it as ... 

Inflorescence

In one of nature's most spectacular floral displays, colonies of cobra plants throughout California and Oregon are covered with eerie red flowers during the months of May through June. A flower bud forming in the rosette center during the cold winter months develops into a tall scape by spring, often reaching a height of 70-80cm. A red solitary flower blooms in May in a pendulous position at the tip of the tall scape.

Though significantly distinct in structure from the pitcher plant flowers of the East, the cobra plant flower seems to exhibit some evolutionary commonality with those of the eastern pitcher plants. (See below for a tiny notch on the petal serving as a pollinator entrance, as in Sarracenia)

The dainty flower has five petals, which hang from the base of the dangling flower. The tip of each petal comes together to form a slightly elongated sphere. Each petal has a small notch on each side two thirds of the way down from the attached base. When the corolla sphere is formed, each adjacent notch pair creates one circular opening, five in all. A pale-yellow petal is heavily lined with red veins, making the flower appear bright red.  Five elongated yellow sepals softly overhang the red corolla. Inside the corolla a bell-shaped ovary hangs at the base.

An insect pollinator enters the corolla through one of the five circular openings. Since the five-lobed stigma projecting under the bell-shaped ovary is located right at the same level as the circular openings, the pollinator is bound to brush the stigma immediately upon entry and deposit the pollen collected from the previously visited flower. Fifteen or so stamens hang around the ovary base inside the corolla. As the insect pollinator ascends in the corolla interior in search of nectar, it now collects pollen of that flower. When the insect is ready to leave the flower, it does so by sliding down the ovary slope and exiting the flower either through one of the circular openings or by pushing the petal tips. It is unlikely the insect will touch the stigma again -- which is somewhat hidden under the expanded bottom of the bell-shaped ovary. This structure seems to encourage cross-pollination and reduce the chance of selfing.

Elusive Pollinator

There is no report of field observation supporting the above pollinator scenario. It is a common observation for those who have visited a colony in September that countless scapes stand in the cobra field, supporting capsules filled with hundreds of viable seeds. Whoever is responsible for the abundant crop of seeds, the unidentified pollinator somehow succeeded in evading discovery for the past 150 years.

Rebecca Austin, through her keen observations, suspected the ever-ubiquitous spider to be a pollinator of cobra plants. In the field, it is quite common to see spiders and their webs in the cobra plant flowers. Indeed, it is often difficult to find a flower totally free of spider web. Glistening silver silk, blowing in the gentle spring breeze, in the blossoming cobra plant colony tells us the complexity of the ecosystem.

Schnell (2002) bets pollination biologists will one day identify a bee to be the yet-unknown pollinating agent for the cobra plants, as for Sarracenia flowers in the East. Rondeau (1995) points out the total lack of investigation on nocturnal creatures.  Some entomologist claims the unpleasant odor of the flower clearly suggests pollination by flies (Rondeau 1995).

Germination & Growth

The May blossom is soon to be followed by a rush of fresh, green, tubular leaves shooting up from the rosette center, signaling the onset of a trapping season in the cobra plant country. These are the first leaves of the season and the tallest of all the leaves for the year.

In nature, the seeds set by September. A tall scape (that reaches a height of 80cm at the time of flowering) grows further after fertilization as it straightens itself from pendulous to erect posture, often reaching 100cm or more in height. Each flower capsule is filled with hundreds of viable seeds. A characteristic seed has numerous tiny, air-filled projections for wind dispersal. Floating seeds in the stream may find new colonies down the stream. The seeds germinate the next spring. One may find tiny seedlings in the field with juvenile leaves which are tubular with a narrow pointed tip.

The cobra plant, for its size, is a rather slow grower.  After germination, it takes two to three years for juvenile, hollow, pointed-end leaves to assume the characteristics of a mature pitcher.  A few more years are required for the plant to flower. The plant continues to grow, producing larger leaves every ensuing year until it reaches its size maturity in 7-10 years from the seedling. 

The cobra plant also shows vigorous vegetative reproduction. The mature plant sometimes produces another growth point in the rosette center, eventually growing into two plants. In addition, the plant habitually produces long stolons, or underground runners. The tip of these stolons develops into a new plant. This ability of the plant to reproduce asexually often results in rather dense growth characteristics as typically seen in the wild cobra plant populations throughout their distribution.

Pollinator/Prey Dilemma

A strange sense of similarity between flower and trap of this species was felt by workers observing the plants in the field. If this dual attractiveness also extends to the insect world, a pollinator/prey paradox may arise. Are the flower and the pitcher designed to attract the same insects? If so, aren't they competing for the same visitors to the plants, leading to a potential pollinator/prey dilemma? Given the average height of a mature pitcher leaf in the range of 40-60cm in nature, a tall scape typically grows to 70-80cm in height. This seems to offer some "spatial" separation between pollination and prey-trapping zones. Although varied depending on the locality and perhaps also on the severity of the previous winter, field observations show a relatively small number of functional traps remain at the time of anthesis. This does offer a "temporary" isolation of a month or so for fertilization, before new pitchers become fully grown and functional -- though I have seen some large colonies in Oregon where pitchers of the previous season were well preserved into flowering.

Anthocyanin-Free Population "Othello"

A population of anthocyanin-free plants has been found in California (Meyers-Rice 1997). The flower has no red venation and is totally yellow. The pitcher is also all-green to yellow, without any red pigmentation. The plants are identical to the normal variety in all the other aspects. Meyers-Rice (1998) gave the plants a cultivar, Darlingtonia californica "Othello". (The cultivar is a "cultivated variety" that is registered with an International Registration Authority, such as ICPS.)   

Compass Plant

It is Rebecca Austin who first reported the compass nature of the cobra plant.  She observed that the plant always produced pitcher leaves in pairs, a total  of 10-18 new leaves each year. The first two large leaves in the spring would face the north-south direction, with the first leaf always being the tallest of the year. The next two would emerge in the east-west direction, thus, the first four pitchers of the season pointing in the direction of the four major axes of the compass, and these four large leaves standing far above all the subsequent ones. Some others confirmed her observations.

Schnell (2002) noted his cultivated plants obeyed this compass rule. He then turned the pot 90 degrees. The plants produced the leaves according to the old orientation in the first year but adjusted to the new orientation the following year.

My field observation confirmed this compass tendency, though occasional violators have been noted. Incidentally, the emerging direction of the leaf (governed by the compass rule) and the characteristic "spin" of the pitcher are two separate things. Thus, the final orientation of the cobra head (or the direction the fishtail appendage points to) is the sum of the initial leaf direction and the leaf twist (90-270 degrees, according to Rondeau 1995). 

Health of Habitat

Some of the large cobra plant habitats are more than 100 years old. "One might expect that the improvement of the soil, resulting from the sustained capture of insects, would result in the competitive invasion of more vigorous species.” Juniper et al. notes, referring to the constant streams flowing on the soil surface, "That this is not the case with Darlingtonia may be due in part to the dynamic nature of its habitat, forever removing the nutrient-rich humus that it produces. In this respect, Darlingtonia differs from its relative Sarracenia and many other carnivores which continually destroy their own habitat."

The rejuvenation benefit of carnivorous plant habitats in general due to periodic, naturally occurring fires is recognized by various authors. Just as in the eastern pitcher plant habitats, Darlingtonia also benefits from the natural fires in their habitats. The low intensity ground fire is said to pose little damage to the established cobra plant colonies.

 ----
*
See Rondeau 1995, for the history of how this unique plant from the West was "named for a man who never saw it, never collected it, and never even visited the golden state!".

**
 Some feel the three genera (Sarracenia, Darlingtonia and Heliamphora) of New World pitcher plants currently comprising the entire family Sarraceniaceae are distinct enough, in terms of both floral and vegetative structures, that the creation of the separate families are warranted.  

*** I have noted that a plant from an underground stolon can have the opposite orientation. My large cobra plant has produced several runners, from the tip of which has emerged a new young plant. Still connected to the parent plant by stolons, two of them exhibit counter-clockwise twist while the rest of the pack, including the parent, all have clock-wise leaf orientation.

 

PHOTOGRAPHY