& J. Bogner
The scientific material in this article was extracted from the published scientific description of Philodendron pusillum by Dr. Eduardo Gonçalves and Dr. Josef Bogner. Many of the photos of our specimen have been reviewed by Dr. Gonçalves. The specimen in all the photos on this page now resides in the collection of the Missouir Botanical Garden as specimen number C.101529.
Published to science in 2004, Philodendron pusillum (pew-SIL-lum) is found endemically (exclusively) in the lowlands of south central Colombia relatively near the border with Brazil. Philodendron pusillum is one of the smallest Philodendron species known to science and is somewhat similar to Philodendron humile which is found endemically near Acre, Brazil. Acre is substantially closer to Peru than to Colombia. Philodendron humile is also a very small species and was also published by Dr. Gonçalves. The major difference in Philodendron pusillum and Philodendron humile is the later has cordate (heart shaped) leaf blades. The name "pusillum" indicates a small leaf. At this writing P. pusillum is considered quite rare in private as well as in public collections.
Philodendron pusillum is found southeast of Bogotá in Colombia's Amazonas Department (similar to a state) in the vicinity of the Colombian river known as Rio Caquetá. The river is near La Pedrera which is found at an elevation of approximately 240 meters (790 feet) above sea level. The region is remote and is not often visited. Other species yet unknown to science are likely yet to be discovered in the area. Although the distance is great, La Pedrera can be found on a map almost half way between Carachi, Ecuador and Manaus, Brazil.
A slow growing species, Philodendron pusillum was described to science by botanists Dr. Eduardo Gonçalves and Dr. Josef Bogner as a small terrestrial aroid which grows on the forest floor, Philodendron pusillum has been placed in Philodendron subgenus Philodendron. The genus Philodendron is divided into three subgenera including subgenus Philodendron, subgenus Meconostigma and subgenus Pteromischum. These subgenera are further divided into sections as well as subsections based on the specific characteristics of a species. As explained in the scientific description for Philodendron pusillum, "The Neotropical genus Philodendron is very variable, comprising woody shrubs to herbaceous climbers. It is divided into three subgenera, and the largest, P. subg. Philodendron, to which our new species belongs, is again divided into several sections (Croat 1997)." The sectional placement of Philodendron pusillum has yet to be determined.
Philodendron species are known to be highly variable and many species may demonstrate slightly different growth forms across their range. As a result the coloration and shapes of the leaves as well other parts of a plant may not not always appear the same. These variations do not indicate a new species despite the fact collectors assume that any variance indicates something "new" to science. Additionally, Philodendron species vary greatly from the juvenile state to an adult specimen as can be seen in some of our photographs. The growth to the adult form is known as ontogeny which simply indicates the plant changes as it matures in the same way human beings mature as they grow from a child to an adult. For a better understanding of natural variations within species please refer to this link: Aroid variation
With almost rubbery coriaceous (leather-like) leaves, Philodendron pusillum grows terrestrially. A fully adult specimen only reaches a height of approximately 30 to 35 cm (12 to 13.75 inches). Growing slowly in clusters with adjoining stems the species produces approximately 4 to 7 leaves per plant with the blades lanceolate to elliptic-oblong in shape. A lanceolate leaf blade is shaped like the knife-like weapon known a lance while a blade that is both elliptical and oblong may possess wider leaves. The leaf blades open from the cataphyll in a supervolute fashion which is similar to convolute vernation. Supervolute has one leaf margin (edge) rolled inward with the opposite margin rolled around it whereas convolute has both margins rolled in the same direction around the midrib and around itself. (see photo, right)
P. pusillum may also produce a reduced foliar leaf which is simply a blade that never matures and perpetually remains small (photo left, below). The blades are acuminate which indicates they taper to a point at the apex and measure approximately 13 to 20 cm (5 to 7 inches) long by 2.4 to 4.5 cm (1 to 1 3/4 inches) in width. The upper blade surface is known in science as the adaxial surface while the lower surface is known as the abaxial side of the blade.
Within aroids and other plant species the veins on a leaf have specific names. The most prominent veins on Philodendron pusillum are the midrib, primary lateral leaf veins and interprimary or secondary veins. The minor veins are known as the tertiary veins. The venation (veins) of Philodendron pusillum is considered to be both parallel and pinnate. Parallel indicates the veins run roughly side by side while pinnate indicates they are formed similar to the arrangement of the fronds of a palm. In Philodendron pusillum that indicates they emerge from the midrib at the center of the leaf (see photo, above left) in a parallel fashion progressing towards the blade's margin (edge). Philodendron pusillum possesses 4 to 5 primary lateral veins on each side of the midrib that extend from the rib toward the margin at an angle of 20 to 30 degrees. There are also 3 to 6 substantially thinner secondary veins which can be found situated between the primary lateral veins. In addition there are numerous much finer tertiary (minor) veins situated between the secondary veins (see photo right, below). The veins are more easily observed on the abaxial surface (underside) of the blade.
The stalks that support the leaves are known as petioles. Despite common misconceptions the petiole is not the "stem" which is a term commonly used incorrectly by plant collectors. The petiole connects the lamina of the leaf blade at the petiole's top to the actual stem at its bottom. The shape of the petioles of our specimen of P. pusillum are round (terete) to "C" shaped with a canaliculate upper surface. Canaliculate indicates the plant has a sulcus or canal-like depression running along the petiole's axis.
The stem is the support for the plant and is where buds form from nodes to produce petioles thus leaves. The nodes also produce roots as well as the peduncles which support an inflorescence thus flowers. A peduncle is the internode between the spathe and the last foliage leaf. The stem is the main axis of the plant and is the plant's base. The majority of the stem of Philodendron pusillum grows above ground and little exists beneath the soil's surface. The purpose of the stem on any aroid is to collect and store water as well as nutrients which are absorbed by the roots and disperse them to the plant. The stem of Philodendron pusillum is rhizomatous (creeping) and grows across the ground and is normally reddish in color. Due to natural variation the stem may not always be red. Dr. Gonçalves explains "Usually it is reddish at the base, but considering (your plant) is cultivated a little change is expected." The roots of Philodendron pusillum are reddish as well as stiff. The roots are are numerous on the lower portion of the stem.
The petioles grow from a bud on the stem and transfers water along with nutrients from the stem to the leaves. The blades then convert carbon dioxide in the air into oxygen for other living organisms such as rain forest animals to breathe The petioles of Philodendron pusillum are typically reddish but may be expected to vary in color in cultivated specimens. As can be observed in our specimen very little red is visible directly on the stem but is enhanced as the specimen matures.
When a new leaf and petiole begin to emerge from a bud at the stem it is surrounded by a bract-like modified leaf known as a cataphyll. The cataphyll is the singular most important identifying characteristic of an aroid. The purpose of the cataphyll is to protect the new leaf as it develops. The cataphylls first emerge as a light green but turn reddish and become somewhat "papery" as they age.
We have observed the cataphylls of Philodendron pusillum to be double keeled (two ribbed) but the ribs are not always obvious until the cataphyll begins to change coloration. The cataphylls are also membranaceous. I asked Eduardo to explain, "Membranaceous means with the consistence of a membrane, i.e. like a piece of your shirt. It is the opposite of coriaceous that is like a piece of leather". A double keeled petiole is typical of species that have a sympodial growth form. The cataphylls of P. pusillum persist on the stem as dried material once the blade emerges and is fully developed. (see photo below).
All Philodendron species are members of the larger plant family known as Araceae and are commonly known as aroids. An aroid is a plant that reproduces via the production of an inflorescence which consists of two distinct parts known as the spathe and spadix as well as the peduncle which provides support. Other near microscopic parts including the sexual parts are known as the male, female and sterile flowers as well as anthers, stamens, stigma and pollen when the plant is in the reproductive process.
Many people believe the spathe is a "flower" which is incorrect. The spathe is a modified leaf whose purpose is to protect the spadix at the center of the inflorescence during its sexual development. The spadix is a spike on a thickened fleshy axis which can produce tiny flowers. When sexually mature tiny flowers can be found along the spadix but the spathe itself is not a flower.
Aroids have two basic reproductive groups. One produces a bisexual inflorescence with male and female flowers mixed together along the length of the spadix while the other is the unisexual group and includes those aroids that produce an inflorescence with separate flower zones.
Philodendron species are unisexual and the female flowers are cleverly hidden inside the lower portion of the spathe in a closed chamber known as the floral chamber. At female anthesis when the plant is ready to reproduce the spadix produces female flowers for a very short period of time (normally one day) near its base. They are followed by male flowers which will produce pollen but normally for only a single day. In Philodendron species the female flowers are produced on the first day followed (normally) by the male flowers on the second. The sterile flowers are also hidden inside the floral chamber just above the female flowers and are a primary attractant to insect pollinators since they are responsible for the production of an attracting pheromone (perfume). The sterile flowers are used as food by pollinating beetles since they contain proteins in the form of lipids. The male flowers are separated in a zone higher on the spadix in order to prevent self pollination. All the flowers are very small and almost microscopic.
female flowers are pollinated by an appropriate insect which is normally a
beetle from the genus
Cyclocephala that carries
pollen from another specimen currently at male anthesis the spadix will
be pollinated and begin to grow berries
(fruits) which eventually contain seeds. The berries are eaten by rain
forest animals and birds and are scattered about the forest in their
Philodendron pusillum produces a solitary (single) inflorescence which is supported on a stalk known as the peduncle. The spathe is small and typically measures 4.5 to 4.8 cm (1.75 to 1.9 inches) in length. The spathe is green while the spadix at its center is only 3.5 to 4 cm (1.4 to 1.575 inches) long and grows on a stipe 5 to 6 mm (less than 1/4 inch) long. A stipe is simply a stalk which grows between the spadix and the spathe itself. The color of the fruits produced once pollinated has not been observed or reported in scientific literature.
For more information on aroid pollination please read this article by aroid expert Julius Boos. Aroid pollination
Our specimen was a gift in 2006 from Florida aroid grower Russ Hammer. My thanks to aroid botanist Pete Boyce in Malaysia for directing me to the correct correct scientific name for the plant shown on this page. Additionally, my deep thanks to Brazilian aroid botanist Dr. Eduardo Gonçalves for examining my photographic material and providing his opinion of the identification of this specimen. Both of these experts have frequently been kind to answer my questions and provide valid botanical information.
The specimen shown in all of the photos on this page now resides in the collection of the Missouri Botanical Garden as specimen number C.101529.
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