Ecological and Taxonomic Distribution of CAM-using Plants
The majority of plants possessing CAM are either epiphytes (e.g., orchids, bromeliads) or succulent xerophytes (e.g., cacti, cactoid Euphorbias), but CAM is also found in hemiepiphytes (e.g., Clusia); lithophytes (e.g., Sedum, Sempervivum); terrestrial bromeliads; wetland plants (e.g., Isoetes, Crassula (Tillaea), Lobelia; and in one halophyte, Mesembryanthemum crystallinum; one non-succulent terrestrial plant, (Dodonaea viscosa) and one mangrove associate (Sesuvium portulacastrum).
Plants which are able to switch between different methods of carbon fixation include Portulacaria afra, better known as Dwarf Jade Plant, which normally uses C3 fixation but can use CAM if it is drought-stressed, and Portulaca oleracea, better known as Purslane, which normally uses C4 fixation but is also able to switch to CAM when drought-stressed.
CAM has evolved convergently many times. It occurs in 16,000 species (about 7% of plants), belonging to over 300 genera and around 40 families, but this is thought to be a considerable underestimate. It is found in quillworts (relatives of club mosses), in ferns, and in gymnosperms, but the great majority of plants using CAM are angiosperms (flowering plants).
The following list summarizes the taxonomic distribution of plants with CAM.
| Division | Class/Angiosperm group | Order | Family | Plant Type | Clade involved |
|---|---|---|---|---|---|
| Lycopodiophyta | Isoetopsida | Isoetales | Isoetaceae | hydrophyte | Isoetes (the sole genus of class Isoetopsida) - I. howellii (seasonally submerged), I. macrospora, I. bolanderi, I. engelmanni, I. lacustris, I. sinensis, I. storkii, I. kirkii |
| Pteridophyta | Polypodiopsida | Polypodiales | Polypodiaceae | epiphyte, lithophyte | CAM is recorded from Microsorium, Platycerium and Polypodium, Pyrrosia and Drymoglossum and Microgramma |
| Pteridopsida | Polypodiales | Pteridaceae | epiphyte | Vittaria
Anetium citrifolium |
|
| Cycadophyta | Cycadopsida | Cycadales | Zamiaceae | Dioon edule | |
| Pinophyta | Gnetopsida | Welwitschiales | Welwitschiaceae | xerophyte | Welwitschia mirabilis (the sole species of the order Welwitschiales) |
| Magnoliophyta | magnoliids | Magnoliales | Piperaceae | epiphyte | Peperomia camptotricha |
| eudicots | Caryophyllales | Aizoaceae | xerophyte | widespread in the family; Mesembryanthemum crystallinum is a rare instance of an halophyte that displays CAM | |
| Cactaceae | xerophyte | Almost all cacti have obligate Crassulacean Acid Metabolism in their stems; the few cacti with leaves may have C3 Metabolism in those leaves; seedlings have C3 Metabolism. | |||
| Portulacaceae | xerophyte | recorded in approximately half of the genera (note: Portulacaceae is paraphyletic with respect to Cactaceae and Didieraceae) | |||
| Didiereaceae | xerophyte | ||||
| Saxifragales | Crassulaceae | hydrophyte, xerophyte, lithophyte | CAM is widespread in the family | ||
| eudicots (rosids) | Vitales | Vitaceae | Cissus, Cyphostemma | ||
| Malpighiales | Clusiaceae | hemiepiphyte | Clusia | ||
| Euphorbiaceae | CAM is found is some species of Euphorbia including some formerly placed in the sunk genera Monadenium, Pedilanthus and Synadenium. C4 photosynthesis is also found in Euphorbia (subgenus Chamaesyce). | ||||
| Passifloraceae | xerophyte | Adenia | |||
| Geraniales | Geraniaceae | CAM is found in some succulent species of Pelargonium, and is also reported from Geranium pratense | |||
| Cucurbitales | Cucurbitaceae | Xerosicyos danguyi, Dendrosicyos socotrana, Momordica | |||
| Celastrales | Celastraceae | ||||
| Oxalidales | Oxalidaceae | ||||
| Brassicales | Moringaceae | Moringa | |||
| Sapindales | Sapindaceae | Dodonaea viscosa | |||
| Zygophyllaceae | Zygophyllum | ||||
| eudicots (asterids) | Ericales | Ebenaceae | |||
| Solanales | Convolvulaceae | Ipomaea | |||
| Gentianales | Rubiaceae | epiphyte | Hydnophytum and Myrmecodia | ||
| Apocynaceae | CAM is found in subfamily Asclepidioideae (Hoya, Dischidia, Ceropegia, Stapelia, Caralluma negevensis, Frerea indica, Adenium, Huernia), and also in Carissa and Akocanthera | ||||
| Lamiales | Gesneriaceae | epiphyte | CAM was found Codonanthe crassifolia, but not in 3 other genera | ||
| Lamiaceae | Plectranthus marrubioides, Coleus | ||||
| Plantaginaceae | hydrophyte | Littorella uniflora | |||
| Apiales | Apiaceae | hydrophyte | Lilaeopsis lacustris | ||
| Asterales | Asteraceae | some species of Senecio | |||
| Magnoliophyta | monocots | Alismatales | Hydrocharitaceae | hydrophyte | Hydrilla, Vallisneria |
| Alismataceae | hydrophyte | Sagittaria | |||
| Araceae | Zamioculcas zamiifolia is the only CAM plant in Araceae, and the only non-aquatic CAM plant in Alismatales | ||||
| Poales | Bromeliaceae | epiphyte | Bromelioideae (91%), Puya (24%), Dyckia and related genera (all), Hechtia (all), Tillandsia (many) | ||
| Cyperaceae | hydrophyte | Scirpus, Eleocharis | |||
| Asparagales | Orchidaceae | epiphyte | The Orchidaceae has more CAM species than any other family (CAM Orchids) | ||
| Agavaceae | xerophyte | Agave, Hesperaloe, Yucca | |||
| Asphodelaceae | xerophyte | Aloe, Gasteria and Haworthia | |||
| Ruscaceae | Sansevieria, Dracaena | ||||
| Commelinales | Commelinaceae | Callisia, Tradescantia, Tripogandra |
Read more about this topic: Crassulacean Acid Metabolism
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