Plant Image Collection
Balanophora is a flowering plant that parasitizes roots of trees. It belongs to a tropical family, Balanophoraceae. This is Balanophora fungosa, on the forest floor of Mossman Gorge, near Cairns in Queensland, Australia. Notice the pale colored modified leaves at the bases of these two shoots. Balanophora is entirely lacking in green pigments.
Each flowering stalk of Balanophora fungosa bears thousands of female flowers (the top portion) and a much smaller number of male flowers near the base of the flowering stalk. About twenty male flowers can be seen on the flowering stalk at left (they have white tips). The flowering stalk at right is older, and the male flowers have faded.
The female flowers on the top half of this flowering stalk of Balanophora fungosa are unbelievably small--they just look like a grains of a white powder. The male flowers have petal-like structures (brownish in color) surrounding the white pollen-bearing portions.
At a higher magnification, details of the male flowers and the female flowers on this flowering stalk of Balanophora fungosa become evident. The surface of the portion bearing female flowers, above, now can be seen to consist of small structures.
A male flower of Balanophora fungosa at very high magnification. Out of focus are a few of the brown petal-like structures. The white globe consists of the structures bearing pollen, the anthers, which have opened and look like papery scales. With a little imagination, you can see white pollen grains among those scale-like structures.
A small portion of the flowering stalk of Balanophora fungosa, showing female flowers at very high magnification. There are two kinds of structures here, which differ in size. The bigger ones are structures that are difficult to name. We don't know what they represent for sure--are they like petals, or are they some other kind of formation? The tiny structures are the female flowers. If not the tiniest flowers in the world of flowering plants, they are close to being the tiniest.
Helosis may look like a fungus, but it's a flowering plant with very tiny flowers. It grows as a parasite on the roots of trees, forming a mound of tissue from which emerge flower stalks (inflorescences). Helosis is native to tropical America, but the family to which it belongs, Balanophoraceae, occurs in tropical areas around the globe. Here are three flowering stalks of Helosis. The one at the right is covered with polygonal scales that fall off. The one at left shows an inflorescence bearing male flowers, which are white and well separated from each other the inflorescence in the middle shows the dense covering of extremely tiny white female flowers.
The orange-colored polygonal scales of the inflorescence of this Helosis (found near Iquitos, Peru) are beginning to fall off. Revealed underneath are tiny white dots--female flowers. They are among the smallest flowers, if not the smallest flowers, of any flowering plant in the world.
Here are the male flowers of the Helosis from Iquitos, Peru. Each flower has three petals (or what appear to be petals) surrounding a group of three united stamens. Filling the male flowers are droplets of sweet liquid. Flies are attracted to these drops. In the process of feeding on the liquid, the flies pick up pollen grains, which they transfer to female flowers.
A Helosis (Balanophoraceae) from Costa Rica. Here are three flowering stalks (inflorencescences) of this species. The one at left is young, covered with polygonal structures that will fall off to reveal the flowers. The large inflorescence in the middle is covered with male flowers, some of which (white) are falling off. The inflorescence at right is covered with female flowers, which are much smaller than the male flowers. If you look closely, you will see a fly visiting the inflorescence in the middle, feeding on the sweet shiny droplets that occur on the male flowers.
Inflorescence of the Costa Rican Helosis. From right to left: an inflorescence still covered by polygonal scales; an inflorescence in which male flowers are beginning to emerge; and an inflorescence from which some scales have fallen, revealing a covering of female flowers. The top of the plant body from which the flowering stalks have emerged is at lower left; it connects with the root of a tree (not shown).
The surface of an inflorescence of a Costa Rican Helosis, showing male flowers among the polygonal scales that have shrunken away from each other. The male flowers are reddish and bear white-tipped stamens. A male flower pulled away and shown on its side is at upper right: two petals diverge, and the stamens are in its center.
The purplish-black scales are falling from the inflorescence of this Costa Rican Helosis, revealing the numerous female flowers underneath. The tips of the female flowers are white.
Hundreds of female flowers cover this flowering stalk of a Costa Rican Helosis. Although no moisture is shown here, droplets of liquid are often found on female Helosis flowers, attracting flies, which also visit the male flowers in search of a similar liquid.
At first glace, this appears to be a picture of a green succulent, Euphorbia caput-medusae, viewed from above the plant--and it is. But next to the gray stone near the bottom of the photo is a brown flower. It belongs to a root parasite, Hydnora africana, which lives on the Euphorbia. Hydnora, from Africa, belongs to a family, Hydnoraceae that also includes a New World genus, Prosopanche. The relationships of this family were quite uncertain, but recent molecular data suggest that Hydnoraceae is a "basal angiosperm," among the more primitive of flowering plants. Parasites are often so highly modified, compared to their non-parasitic relatives, that their relationships are difficult to determine.
The only portion of Hydnora that appears above the ground surfaces is the upper portion of the flower. Much of the flower is below the soil surface. The flower is thick and succulent in texture. The portion of the flower above the ground surface is tubular and has three openings, one of which is shown here. There are three thick structures, which botanically should be called perianth segments, and which might be likened to sepals, that tend to stay united at the top of the flower.
A plant of Hydnora and the two Euphorbia plants to which it is attached have been excavated and washed. This Hydnora plant is the only one ever known to have been cultivated. The seeds were collected in the Karroo Garden, Robertson, South Africa, by Sherwin Carlquist in 1973, and brought back in a fresh condition to his home in Claremont, California. He purchased several rooted cuttings of Euphorbia caput-medusae, a known host plant for Hydnora africana, removed the Euphorbia plants from their pots, lined the pots with Hydnora seeds, and put the Euphorbia plants back into their pots. During the next several years, the Euphorbia plants were repotted, but noting appeared to have occurred. The Euphorbia plants were planted into the ground. In 1979, a flower of Hydnora appeared. Apparently the development of a seedling of Hydnora is slow. Also, the development of the Hydnora may have accelerated when the plants of Euphorbia were planted into the ground and thereby enlarged in size beyond the size they had when potted. In this photograph, portions of two of the Euphorbia caput-medusae plants are shown. The roots of the Euphorbia are white, and thereby they are easily distinguished from those of the Hydnora, which are dark brown. The plant of Hydnora consists of thick succulent roots. Hydnora has no stems. The flowers of Hydnora are borne on the surfaces of the roots.
A longitudinal section of a flower of a flower of Hydnora africana from the cultivated plant. Notice that the flower is attached to the horizontal, knobby brown root (horizontal, at the bottom of the picture). At the top of the flower are two of the "sepals" (perianth segments) that can be seen above the surface of the ground. They are orange inside. Just below where these are joined is a short tube. At the top of the tube, one can see some yellowish-orange structures protruding into the tube. These are two of the three anther-groups. Hydnora flowers don't have stamens in the ordinary sense. There are groups of anthers united into bunches. At the bottom of the tube is a stigmatic area. The basal part of the flower has a cavity in it. At the top of the cavity are white ovules. The ovules will mature into seeds. The flower of Hydnora is a kind of intricate trap. Or, as we will see, a temporary trap.
The flower of Hydnora, when it first opens, has white threadlike structures that cross the gap between the "sepals." The openings between these threads are barely large enough for a beetle to enter. More about that later! Although a beetle may enter a flower, it evidently has difficulty in finding its way out of the flower. This keeps it inside a flower long enough so that the beetle can pick up pollen or deposit pollen on its surface onto the stigmas at the bottom of the floral tube.
The threads that cross the gaps between the "sepals" of the Hydnora flower when the flower opens are pulled apart after a few days. Any beetles that entered the flower through those threads can now easily escape.
The inside of each of the three parianth segments (like sepals or petals) of Hydnora africana. Notice the bright organ color of these structures. On them are downwardly pointing hairs that are effective in directing beetles down into the lower portions of the flower, slowing the beetles from escaping from the flower. In this respect, Hydnora flowers are like the leaf of a pitcher plant (Sarracenia). The beetles are attracted to the flower of Hydnora by the scent emitted by the ivory-colored pad of tissue in the center. It emits an unpleasant dung-like odor. Not surprisingly, the beetles that are attracted are dung beetles. Even though this flower was on a plant cultivated in California, half a world away from where the plant is native in Africa, it attracted dung beetles. Very likely not the same kind of dung beetles as in Africa, but related. The pollination mechanism that occurs in the native habitat in Africa was thus duplicated, amazingly, in the cultivated plants.
Here are two of the three anther-masses or anther groups of the Hydnora flower. They are arranged in a triangle; a gap between their pits permits beetles to fall down onto the stigma. The anther groups shown here have not yet released pollen. The stigmas of this flower are probably receptive at this time, however. Thus, beetles that have pollen on their bodies from an older flower would be able to brush some of that pollen onto the stigmas of this flower, achieving cross-pollination.
Here are the dung beetles that visited the Hydnora flowers of the plant cultivated in Claremont, California in 1979. Notice their bodies have some whitish hairs on them; pollen could adhere to these hairs. Flowers pollinated by beetles usually have some tissue that offers beetles as food. In Hydnora, that's the whitish tissue on the inside of the "sepals." But beetles don't confine their feeding to such special "bribe" tissues. Beetles eat pollen and then eat the cells of the stigma. Beetle-pollinated flowers usually have an abundance of pollen and an abundance of stigma areas, and Hydnora flowers are no exception. By producing excess pollen and stigma cells, beetle-pollinated flowers succeed in achieving pollination and producing seeds despite the feeding habits of the beetles.
A root of Euphorbia (white) growing alongside a Hydnora root has been "captured" at several points. The Euphorbia roots form pad like structures. The contacts between the Hydnora and the Euphorbia are thereby widened. The Euphorbia furnishes Hydnora with moisture, food, and all other substances. Hydnora is not green and is completely dependant on a host plant. Succulent underground portions of the Hydnora, however, may fragment and stay alive for indefinite periods of time. Those fragments may at some time be able to contact a Euphorbia root and begin growth again.
A Hydnora africana that has numerous contacts with a Euphorbia root. The nature of the underground axis (stem or root?) in Hydnora is not easy to determine with certainty, because there are no close relatives of Hydnora, and Hydnora is highly specialized for parasitism. However, there are reasons to favor the concept that the Hydnora axes are roots rather than stems. The growing tips show no evidence of reduced leaves at all, and there are no reduced leaves adjacent to the bases of the flowers. The five or six longitudinal rows of stubby roots on the axis remind one of patterns of lateral root formation on roots, whereas lateral roots that form on stems of plants don't tend to form neat longitudinal rows. And flowering plants other than Hydnora that are root parasites form roots (as in Orobanche), not underground stems, that interconnect with roots of host plants.
There are about 100 species of Orobanche (common name: broomrape) worldwide, mostly in temperate areas. Orobanche is a parasite on the roots of other plants. Orobanche has no chlorophyll. The flowers suggest flowers of penstemons, monkey flowers, or snapdragons, and Orobanche is closely related to those plants. However, Orobanche goes into a family, Orobanchaceae, that now also includes Indian Paint Brush (Castilleja), which is a green plant that parasitizes roots of other plants. Some species of Orobanche are rare, but some are common and even pests. Orobanche ramosa is a serious parasite on tomato plants in California.
Two plants of Orobanche fasciculata that have been excavated. Notice that the lower two-thirds of the plants is white: this portion of the plants is underground, and the upper one third of the plants appears above the soil surface. The leaves of these plants are narrow and cover the stems. Some of the leaves have turned brownish. Although white when first formed, the leaves can turn brown because of injury or even natural pressure as the flowers expand and push upward through the soil surface.
At the bases of these two plants of Orobanche fasciculata are roots; especially note the plant at the right. These roots belong to the Orobanche plants, but they have interconnections (not shown) with roots of host plants. Orobanche takes water, sugar, and other substances from host plants through their roots.
The flowers of Orobanche fasciculata are yellowish. Flowers of other species of Orobanche range from purplish to ivory-colored to an orange color.
A flower of Orobanche californica, sectioned so as to show two of the four stamens. The pollen has mostly been shed from the pale yellow-colored anthers at this stage. The stigma is white and has two pointed flaps.
Ammobroma (Greek for "sand food") is the common name for this curious desert sand dune plant, a flowering plant parasitic on desert shrubs such as Tiquilia and Eriogonum. The only part of the plant normally visible above the sand surface is the inflorescence, which is 5 to 15 cm in diameter.
The scientific name for Ammobroma is Pholisma sonorae--it was originally named Ammobroma sonorae, but it is now thought to belong to the genus Pholisma. Pholisma was said to be in the small family of parasitic plants Lennoaceae, but now Lennoaceae is considered a subfamily (Lennoideae) of Boraginaceae, the forget-me-not family. This is a smaller inflorescence, which looks doughnut-like in shape, but is actually funnel-shaped, the outer edges of the funnel rounded, and the center of the funnel filled with sand.
A larger inflorescence of Pholisma sonorae, showing the somewhat irregular shape. Pholisma sonorae grows in sand dunes of northwestern Sonora, Mexico ("El Gran Desierto") and adjacent California and Mexico. The name "sand food" derives from its apparent use by Sonoran natives as a source of food.
Normally the inflorescence of Pholisma sonorae is in contact with the sand. This individual is probably abnormal in that respect because sand has blown away.
An inflorescence of Pholisma sonorae removed from the sand, with the sand shake from it reveals that the inflorescence is funnel shaped. The center is older; flowers are progressively younger toward the edge of the inflorescence.
A somewhat younger inflorescence of Pholisma sonorae, removed from the sand, with the sand shaken from the center. The flowers are lavender in color. Perhaps one should say heliotrope colored, because Pholisma sonorae is now considered a member of the Boraginaceae, sometimes known as the heliotrope family.
A view of an inflorescence of Pholisma sonorae from the side. Notice that the hairs of the inflorescence, from which the flowers emerge, are the same tan color as the sand in which Pholisma sonorae grows. This color may prevent Pholisma sonorae eaten by desert herbivores. Herbivores tend to avoid plants that are excessively hairy.
An inflorescence of Pholisma sonorae removed from the sand and positioned so that the lower side and rounded edge of the funnel-shaped inflorescence are visible. The funnel-shaped inflorescence tapers into the stalk (not shown) which would be at lower right. Notice the small reduced leaves on the lower (outer) side of the inflorescence.
A section down the middle of the funnel-shaped inflorescence of Pholisma sonorae. The edges touch the sand in a living plant, and the depression in the middle is filled with sand.
A face view of a flower of Pholisma sonorae. There are about twice as many flower parts as in the ordinary borages, such as forget-me-not and heliotrope. The color and shape of the flowers suggests that they might be pollinated by long-tongued bees, but no studies have apparently been done on that yet. The sepals turn dark brown very quickly. There are numerous light brown wooly hairs on the sepals.
A section of the edge of an inflorescence. From right to left: old flowers, the floral tube wilted by the bottom widens as seeds form; then a few open flowers; then, at left, the curled over portion of the inflorescence with unopened flowers, the sepals of which are purple.
A longitudinal section of an open flower, with some other flowers nearby. The tissues of Pholisma sonorae are white, but they turn brown with age or soon after being cut. This photograph shows the tubular nature of the Pholisma sonorae flower. The purple sepals are slender, and are covered with large numbers of hairs.
The base of an old flower has been torn open in this photograph, revealing the very small seeds. The seeds are oval and somewhat sticky. What disperses these seeds in the wild is not known.
The underground portions of Pholisma sonorae are long, succulent stems that bear elongate leaves, some of which have been displayed in this portion of a stem dug up from the sand. If one dug deeply enough, one might be able to find where a root connection originally formed between the parasitic Pholisma sonorae plant and its host plant. However, sand continually sifts over Pholisma sonorae plants and buries them more deeply. We have no idea how many flowering stems might branch from one original plant. There is, however, a curious feature shown in this photograph. Apparently the leaves of Pholisma sonorae bear small root like structures on their outer surfaces. Are these indeed roots that make contact with roots of a host plant? They seem unlikely to be hairs of any sort, because the lennoid plants related to Pholisma sonorae have no hairs on underground leaves. However, no studies have been done on these structures, which do not appear to have been mentioned in literature on Pholisma sonorae.
There is a group of non-green flowering plants that is related to the heaths (blueberries, cranberries, rhododendrons) and is often included in the heath family (Ericaceae). This group of non-green plants is a subset of the heath family. Let's call them the monotropoids. Are they parasites? Yes, but in an unusual way. The monotropoids were thought to be "saprophytes." A saprophyte lives on dead plant or animal material, but the monotropoids don't do that. They are parasites on fungi, we can call them mycoparasites. But they don't kill the fungi. The fungi infect the short, stubby roots of the monotropoids, and transfer food and water into the roots. The fungi live in the dense litter of dead leaves in wet forests.
Allotropa virgata, the sugar stick, is a parasitic plant related to the Indian Pipe, the Snow Plant, and the other species in the subfamily Monotropoideae of the heath family, Ericaceae. Like the others, Allotropa is parasitic on fungi that occur in leaf litter beneath conifers. Allotropa is found beneath pines and first is the Sierra Nevada and northern Coast Ranges of California, and it extends northward to the Cascade Range of Oregon and the Olympic Range of Washington. The plants in this photograph are young, and only a few of the many flowers have opened at this point.
Most of the flowers are open on these plants of Allotropa. The flowers turn upward or outward, and that accounts for the name Allotropa, which in Greek means "turned differently." The flowers of the other monotropoids, such as Indian Pipe or the Snow Plant, point downwards.
This picture shows the red and white stripes of the Sugar Stick plant clearly. One authors says that the plants are red with white stripes. But aren't they really white with red stripes? The leaves of the plant are white, which suggests that perhaps the plant is basically white.
- The flowers of Allotropa are white but turn brown quickly. Each flower has give sepals, but no petals. That's why you see the reddish stamens so prominently here. The tips of the stamens point toward the center of the flower.
In the Allotropa flowers pictured, the sepals are still white. The stamens are bright red, and the stigmas, in the center of the flower, are very dark red and shiny.
- The fruits of the Sugar Stick, Allotropa, are rounded and crowded on the stem. The fruits are dry and papery at maturity, and the tiny seeds fall out through the slits on the sides of the fruits.
This dark purple plant is Boschniakia strobilacea. It's sometimes called ground cone, perhaps because the incurved purple leaves make the plant look like a cone--but above each leaf is a flower. Boschniakia belongs to the Orobanchaceae (broomrape family). Boschniakia has no chlorophyll, and is parasitic on the roots of members of the heath family such as arbutus, manzanita, and salal. Boschniakia has no roots, and a large thick base attaches directly to the roots of the host plant.
The flowers are similar in shape to those of snapdragon, and the family to which Boschniakia belongs, Orobanchaceae, is closely related to the family to which snapdragons and penstemons belong (Scrophulariaceae). Also, some partially parasitic flowering plants that are green, such as Indian Paint Brush (Castilleja) now are placed in Orobanchaceae. There are four species of Boschniakia. They occur in northwestern North America and in northeastern Asia.
The seeds of Boschniakia are very small. They are greatly enlarged in this photograph, which shows that the seed surface consists of interlocking polygonal ridges. This structural feature probably helps them in dispersing, perhaps in wind, but there has been no study done on how Boschniakia disperses or how these seeds would behave in a current of air.
Hemitomes congestum, the so-called Gnome Plant, is one of the rarest of the monotropoids--the group that includes Indian Pipe and the Snow Plant. You're lucky to see Hemitomes. It's rare, and it's small-only three or four cm tall when in flower. Sometimes it's pale pink in color.
Sometimes Hemitomes congestum is rose rather than pink in color. It grows in the leaf litter of conifer forests from central California to Washington. The redwood belt in California is a good place to look for it, but it probably grows on fungi in the leaf litter not of redwoods, but of conifers that grow with the redwoods.
Seen from above, the flowers of Hemitomes congestum have four, sometimes five petals (united at their bases) which are fringed and curve outwards. The yellow stigmas are prominent in these flowers.
A flower of Hemitomes congestum with two of the petals removed so that the parts of the flower are visible. From top to bottom: the shiny yellow stigma, surrounded by the anthers, now open and shedding pollen; the hairy filaments on which the anthers are borne, and, at the bottom, the knob like nectaries, structures on the ovary that secrete nectar.
The upper portion of a flower of Hemitomes just as it opens reveals that the anthers are still closed, but the yellow stigma is sticky and looks receptive. If this is true, the flower would have to be pollinated by pollen from another flower. That's a way in which cross-pollination between plants could be achieved. Nobody knows what insect pollinates Hemitomes.
The stamens and stigma of Hemitomes, surrounded by petals. A sepal is at the left. The anthers are shedding pollen grains, which cling together in irregular groups rather than separate. The sticky nature of the pollen grains helps them adhere to hairs on an insect.
A flower of Hemitomes seen from above. The large yellow stigma is conspicuous. The very hairy nature of the inside surfaces of the petals is also evident. Why such a hairy flower? The hairs might keep small insects from climbing down into their flower and robbing the nectar. In that case, we would expect Hemitomes flowers to be pollinated by a long-tongued insect like a moth. The tongue of a moth could reach through the hairs down to the nectar at the bottom of the flower.
At the base of the flower of Hemitomes (two petals removed), one can see the knoblike nectaries between the hairy white stamen bases. The nectar secreted by these nectaries forms pools in the bases of the petals. A moth might be able to see the light colored flowers of Hemitomes even under relatively dark conditions.
The fruits of Hemitomes congestum are round, white, and fleshy. Because the fruits are fleshy at maturity, presumably they are eaten by some animal which thereby scatters the seeds in various places in the forest litter. But nobody knows what animal eats the fruits.
Monotropsis odorata, the Pygmy Pipes, is a small species of monotropoid that grows in pine woodlands of the southeastern US, mostly in the Appalachian Mountains. It occurs from Maryland south to Florida and east to Kentucky and Tennessee. This picture was taken by Dr. Gary Wallace in North Carolina.
The flowers of the Pygmy Pipes, Monotropsis odorata, have papery brown sepals that sheathe the flowers as the plants come up through the litter of forest leaves.
These dissections of flowers of Monotropsis odorata show the distinctive pale purple color of the petals, which are united into a bell-shaped tube. Ten stamens are present in the flowers, as can be seen from the upper flower, from which the petals have been removed.
Between the purplish bases of the stamens are knob-like nectaries, which secrete nectar that collections in the saclike petal bases.
The central parts of a flower of Monotropsis odorata. The stigma, which collects pollen, is sticky (here, it has collected some debris, unfortunately). The anthers have shed most of their pollen grains. The anthers shed the pollen grains through oval-shaped openings.
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