Pilostyles: An Amazing Wildflower

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Addendum: Pilostyles Is Not The Smallest Flowering Plant

The Undisputed Smallest Flowering Plant In Anza-Borrego Desert

Members of the duckweed family (Lemnaceae) are the undisputed smallest flowering plants. Evidence from DNA analysis now shows that this family is actually a subfamily within the arum family (Araceae). There is a collection of Lemna aequinoctialis (originally cited as L. perpusilla) from Vallecitos Canyon in Anza-Borrego Desert State Park made by Dr. Elias Landolt (1957), the world authority on duckweeds. I have also found this species in several creeks and rivers in Baja California. Whether it still occurs in perennial creeks of Anza-Borrego remains to be seen. It is relatively easy to determine from dried herbarium specimens by its winged root sheath. It commonly flowers and produces minute fruits called utricles. Lema valdiviana is also reprted from Vallecitos Canyon; however, this species is often misidentified. Another duckweed reported from the Anza-Borrego Desert Region is L. turionifera. This unique duckweed produces starch-filled overwintering bodies called turions.

Duckweeds (Lemna) are the smallest flowering plants in the Anza-Borrego Desert region.

The duckweed Lemna turionifera produces dark, overwintering bodies called turions.

Left: Dorsal view of homogeneous population of Lemna turionifera. Some plants have a row of 3-7 minute papules along the midline of the dorsal surface (resembling a row of white dots). In this sample, there are no other visible characters to separate this species from L. minor. No reddish anthocyanin has developed on the ventral surface (near the junction with root base), probably because of the time of year (March 2003). In addition, no overwintering turions are visible because they are usually produced during the fall months. In general, L. turionifera appears to be more common than L. minor in San Diego County, particular in the mountains and inland valleys. This species could be confused with nongibbous L. gibba, but that species generally lacks the dorsal row of papules and often develops anthocyanin on its upper side. Right: Another sample of L. turionifera showing blotches of reddish anthocyanin on its underside (ventral surface). L. minor is very similar; however, it lacks the reddish underside and the dorsal row of papules.

Landolt, E. 1975. "Morphological Differentiation and Geographical Distribution of the Lemna gibba-Lemna minor Group." Aquatic Botany 1: 345-363.

Herbarium specimen of Lemna aequinoctialis from the Sierra San Francisco of Baja California compared with the head of an ordinary straight pin. This view shows the basal root sheath with two lateral wings and a one-seeded fruit (utricle) protruding from a lateral budding pouch. The number of longitudinal ribs on the seed (faintly visible through the transparent pericarp) indicates that this species is L. aequinoctialis and not L. perpusilla. The pin head is (1.5 mm in diameter).

Lemna valdiviana in the shade beneath the willow thickets along Coyote Creek (near 3rd crossing at Lower Willows). Some of the plants were submersed under other vegetation. The closely-related L. minuta typically grows on the water surface, not submersed.

Another ventral view of Lemna valdiviana showing a single vein that extends 3/4 of the distance between the node (point of root attachment) and apex of the plant body. According to Landolt, this is one of the most reliable characteristics to separate it from L. minuta because of the variability of these two species under different growing conditions.

There is little doubt that the single vein extends 3/4 of the distance between the node (point of root attachment) and apex of the plant body. Therefore, this duckweed must be Lemna valdiviana.

The Following Minute Flowering Plants Occur In The San Dieguito River Below The Lake
Hodges Dam. They Have Not Been Reported From The Anza-Borrego Desert Region.

Candy sprinkles compared with a thimble filled with wolffia plants (mostly Wolffia columbiana). The average diameter of a globose wolffia plant body is about 1/25th of an inch (1 mm). To appreciate their minute size, wolffia plants are comparable in size to the multicolored candy sprinkles used for decorating cakes and cookies.

Left: Dorsal view of several budding Wolffia borealis in full bloom. The floral cavity on the dorsal side reveals a circular concave stigma (nearest the basal end) and a single, pollen-bearing anther. Unlike Lemna, Spirodela and Landoltia, the flower is not enclosed within a membranous spathe. The flowers are protogynous, with the stigma becoming receptive before the anther matures and sheds pollen. The far right plant shows only the stigma, while the far left plant shows only the anther. The top and bottom plants show both the stigma and a faint anther. As of 21 January 2010, no wolffia plants have been reported from Anza Borrego Desert. Right: Lateral view of flowering Wolffia borealis showing the dorsal floral cavity containing one anther-bearing stamen and one pistil (gynoecium). The pistil has a seed-bearing ovary, a slender (short) style and a circular, concave stigma. The flowers are protogynous, with the stigma becoming receptive before the anther matures and sheds pollen. A daughter plant protrudes from a funnel-like budding pouch at the basal end. The entire flowering plant is only one millimeter (1/25th of an inch) in length. It weighs approximately 200 micrograms (roughly 1/150,000 of an ounce).

A budding Wolffia borealis in full bloom. The floral cavity on the parent plant contains a minute pistil (gynoecium) with a circular concave stigma and a single stamen with a minute pollen-bearing anther. The plant is compared with the tip of an ordinary sewing needle and a cubical grain of ordinary table salt (NaCl). Three grains placed side-by-side are approximately 1 mm in length.

The World's Smallest Flowering Plant

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