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Zamia floridana

Z. floridana exported to India

Introduction

Zamia floridana is a small cycad native to Florida, United States, especially in its east coast, and can also be found in Southeastern Georgia. Unlike some cycads, its leaves do not have sharp edges. This plant reaches up to 4 feet in height, resembling a small palm tree. It contains neurotoxins and carcinogens, and is poisonous to herbivores and other primary consumers unless it is properly prepared by water-leaching the stems, removing the poisonous glycoside. The plant's underground stem, called a caudex, and roots are usually harvested and consumed for starch by local Indians in Florida. This practice, along with urban development, has driven this plant to become endangered. Evergreen leaves, also referred to as fronds, and cones are found at the terminus of the caudex. Its leaves can vary from wide leaflets to narrow leaflets, depending on its environment. Growing conditions are different for these two types of leaves, with narrow leaflets occurring under high sun exposure.

Alternate names

This plant has several common names. It is known as Florida arrowroot or Seminole bread due to the edible starch derived by Native Americans and early colonists. The preferred name is Coontie, and other variations of its spelling (conti, contihateka, coonti, konti, koontie).

Numerous botanists have proposed several names for Z. floridana, such as Z. integrifolia, Z. pumila, and Z. umbrosa. Subtle differences in leaf size and shape, as well as varying geographic ranges, caused taxonomists to delineate these coonties into those four species.

Morphology

Reproductive Structures

The cone, also called a strobilus, of Z. floridana is dioecious. The male strobilus and the female strobilus are found on two separate plants. The cones on the female plant are thick and have red-orange seeds. They also have a velvety texture, and only grow up to 6 inches. On the other hand, the ones on the male plant are narrow and tall, and contain pollen. They can reach a length of 7 inches. Female cones are usually borne singularly, whereas male cones grow in groups or clusters. The growing season of Z. floridana is during the spring, and the sex of the plant is undetermined until cones are produced.

Z. floridana female cone

Zamia species often produce more than one cone close to the tip of the stem or at the terminus of the caudex where it intersects with the aboveground stem. The multiple cones of Z. floridana may develop through three methods: sympodium, forking of the bundle system, and adventitious buds. The most common form of development is the rapid formation of cone domes, which are "dome shaped vascular supply of the strobili," on the plant's main axis, also known as sympodium. More cones are present when there is a "branching" of the bundles to the cones. The forking of the bundle system starts near the base of a terminal cone that remains erect. The last method is the appearance of adventitious buds "in the cortical tissue that is closely connected with the stelar system of the trunk." These buds then continue to develop similar to typical stems.

Pollination

Z. floridana plants are pollinated by two species of weevils, Rhopalotria slossoni and Pharaxonotha floridana. P. floridana pollinates the plants by using the pollen-bearing strobili as food for its larvae, transporting the pollen with it. The plant can regulate the mutualistic interaction by making the seed-bearing strobilis poisonous to these larvae. On the other hand, R. slossoni does not consume the pollen, but rather, takes shelter in male cones where they become dusted with pollen. They then carry over these pollen into the female cones, which become pollinated. Although the female cones are not consumed, there is evidence of healed scars seen as punctation in the interior of the cone, which are suspected to be caused by weevils.

Toxins

Just like all cycads, Z. floridana produces allelochemicals such as nitrogen-containing methylazoglucosides cycasin, macrozamin, and other neocycasins. Azoglucosides are specific and ubiquitous to cycads. In mammals, cycasin is cleaved to methylazoxymethanol (MAM), causing acute intoxication, mutations, and tumor initiation. MAM is an active mutagen, and hence cycads avoid autotoxicity by storing it as an inactive glycoside in vacuoles. Another cycad toxin is a non-protein derivative of alanine known as BMAA. BMAA in high concentrations is neurotoxic for mammals and chickens and is a likely cause of neurological disorders for humans. It is permanently stored in idioblasts of female cones, whereas it is only released later in male cones. One more non-protein amino acid found in cycads is 2,4-diaminobutyric acid (DABA).

Ecology

Consumption

Parasitism

Three of the most common pests of Z. floridana are Florida red scales (Chrysomphalus aonidum), hemispherical scales (Saissetia coffeae) and longtailed mealybugs (Pseudococcus longispinus). When infested, the plant's growth is stunted, and it becomes covered with blackish mold. Infestations are not limited to one species; several species can be found on the same plant.

Herbivory

When feeding, Rhopalotria beetles avoid consuming the toxins produced by Zamia plants by biting off the trichomes first from the surface of the sporangia-bearing leaves, also known as sporophyll, before actually eating the leaf.

Mutualistic Interactions

Mealybug destroyers, Cryptolaemus montrouzieri, are commonly found on Z. floridana. They form a mutualistic relationship by providing the plant protection from pests in exchange for food. They feed on the coonties' natural enemies, scales and mealybugs, thereby reducing the need for pesticides.

Z. floridana is the host plant for the larvae of Eumaeus atala, also known as atala butterflies. The plant provides food that the caterpillars need for growth and metamorphosis by selectively feeding of starch-rich parenchymal and protein and toxin-filled idioblasts. The atala butterflies can tolerate the toxins produced by coonties until these accumulate. This allows them to practice aposematic protection in which the bright colors on their wings warn potential predators of their toxicity. Cycasin in E. atala can deter its predators due to its unpalatability, and this protection can be strengthened by pyrazines. However, this chemical defense is ineffective to some insects like Seiractia echo. This could have been a parasitic relationship if it weren't for the fecal droppings of caterpillars, which serve as fertilizers that enrich the nutrient-poor habitats of coonties.

Cycasin levels in cocoons of Eumaeus butterflies who consume Zamia plants were analyzed in a study. It was found that these pupal cases have a high concentration of BMAA, one of the toxins produced by cycads, which was believed to provide protection to the larvae. This was because cocoons are made using feces of weevils and larvae, which are rich in toxins since idioblasts are not digested by these insect herbivores.

Nitrogen-fixing Symbiosis

Since Z. floridana is a cycad, which is the only gymnosperm that forms nitrogen-fixing associations, it depends on microbes as a source of nitrogen. It forms a symbiotic relationship with nitrogen-fixing cyanobacteria, which live in its root nodules and are green in color despite not actively photosynthesizing. The filamentous cyanobacteria belong to the genus Nostoc, which is able to form symbiosis with a wide range of organisms. Nostoc inhabits the mucilage in the microaerobic and dark intercellular zone in between the inner and outer cortex of coralloid roots. This zone is transversed and connected by elongated Zamia cells. Coralloid roots are similar to lateral roots, but highly specialized to contain cyanobacteria.

While there haven't been many studies that explore nitrogen-fixing associations in Z. floridana, these have been studied in other cycads. DNA sequence analyses of the tRNA^Leu (UAA) intron and polymerase chain reaction (PCR) fingerprinting of coralloid roots collected from the genera Cycas, Encephalartos, and Zamia showed that cyanobacteria, including a Nostoc strain, were present. Amplified 16S rRNA gene sequences of cyanobacteria found in Cycas revoluta (Cycadaceae) were used to investigate cyanobacterial diversity through denaturing gradient gel electrophoresis (DGGE) and sequence analyses. Similar to Z. floridana, C. revoluta also grows in rocky and sandy coasts. The results showed that there are multiple strains of cyanobacteria, specifically three Nostoc strains, present in a single coralloid root. This study used cyanobionts from cycads grown in natural habitats, and so it's hypothesized that cycads cultivated in controlled environments, such as greenhouses or gardens, have cyanobacteria lower in genotypic diversity compared to those of cycads grown in a natural habitat.

Mycorrhizal Symbiosis

Other cycads closely related to Z. floridana, such as Z. pumila, also form mycorrhizal associations to obtain limited resources. In one study, roots were collected after planting seedlings of Z. pumila in unsterilized native sandy soil and were used to observe for the presence of arbuscular mycorrhizal fungi (AMF). AMF are typically needed by legumes so that their Rhizobium nodules can fix nitrogen in soils where phosphorus levels are low. Phosphorus deficiency can result in the inhibition of nodule production and nitrogen fixation. It was found that there were both septate and nonseptate fungal hyphae present "on the surface of the root cap and on the epidermis and root-cap fragments farther behind the apex" of Z. pumila, with more nonseptate fungal hyphae occurring within and between cortical cells. There was also an abundance of intercellular hyphae and arbuscules formed in the middle cortex. However, there weren't any fungal hyphae in the cortical regions of the coralloid roots lacking Nostoc. Therefore, it is possible that cycads may also need AMF with their nitrogen-fixing coralloid roots to enhance uptake of phosphorus, especially since their habitat is often limiting in phosphorus. The habitat of Zamia is also seasonally dry, and hence AMF may improve water availability, which is beneficial for "plants with poorly developed root hairs." When the dry mass of Z. pumila was measured after exposure to two treatments, the addition of AMF and/or more phosphorus, it was determined that the mass was greater than that of the controls. This indicates that although Zamia does not need AMF when phosphorus level is high in the soil, the accumulated phosphorus was higher in the plant with AMF than in a non-mycorrhizal one.

Horticulture

Z. floridana inhabits well-drained sandy or loamy soils, commonly growing in pine rocklands and hammocks where the soil is moist, but it can live without too much water once established. It can grow in soils low in organic material, although it prefers nutrient-rich soil. It is intolerant of flooding, especially with high salinity. It thrives in dry areas where wildfires are common, but survives due to its underground stem that allows it to grow new leaves.

Effects of varying irradiance levels

To test for optimal growing conditions, one-year-old Z. floridana seedlings were cultivated in 30% and 50% light-exclusion shadehouses for one growing season. The amount of fertilizers used for all treatments were kept constant so as not to significantly affect the results. It was determined that 30% shade is the optimal amount of light in which Z. floridana can efficiently thrive. When grown in 30% shade, the plants had larger caudex and more leaves compared to those grown in direct sunlight or a deeper shade. It seems that caudex size is directly correlated to leaf number; the larger the caudex, the higher the number of leaves. However, those grown in the 50% shade had longer leaves.

Effects of fertilizer

The presence of ammonia in the soil means that nitrogen is readily available for the plant, and hence, cyanobacteria is no longer needed for nitrogen fixation. However, a study found that fertilizers containing a higher percentage of ammoniacal N is beneficial to Z. floridana due to the ability of coralloid cycad roots to fix nitrogen. The authors did not provide any explanations as to why this is the case for Z. floridana. It is recommended to use fertilizers with micronutrients to prevent micronutrient deficiency, which is common for Z. floridana in nurseries and landscapes.