Family Ericaceae

The Ericaceae family consists of about 80 genera and more than 4500 species. This family is subdivided into 8 subfamilies: Ekinathoidae, Monotropoideae, Arbutopideae, Cassiopoideae, Ericoideae, Harrimanelloideae, Styphelioideae, and Vaccinioideae. Most of the species form the genus Rhododendron (about 1000 species) and Erica (with about 700 species). Members of the Ericaceae family are shrubs, subshrubs, or, less often, woody trees, and rarely herbs (Figure 1). They are perennial plants. While nearly all perform photosynthesis, and therefore they are autotrophs, some examples exist of heterotrophic species that lack chlorophyll. At least four species have been found in South America to be epiphytes (living on trees).

Stem

The stem is upright, decumbent, or prostate and may bear trichomes. The pith of the stems is solid (it is formed of tissues).

In young stems, chloroplasts are observed in the parenchyma cells of the cortex and in the parenchyma of the vascular bundles. Cells containing oxalate crystals are also present in some of the cortical parenchyma cells.

The trunk has uniseriate rays. There may be a layer of parenchyma and a layer of sclerenchyma fibers outside the secondary phloem. The bark’s felogen forms from the parenchyma outside the phloem during secondary growth.

Leave

The leaves usually appear on the main stem, as well as on the branches. Its organization can be alternate, pseudowhoriclid, or verticilid, sometimes opposite. They are simple leaves without stipules, usually perennial. The petiole may be absent. The leaves have a serrated or entire margin, flat or scrambled towards the ventral (abaxial) part.

Flower

They appear in a very diverse way, organized in clusters, umbels, corymbs, panicles, fascicles, spikes or solitary. The flowers are hermaphroditic, with radial symmetry (actinomorphic). They do not have hypantium.

The corolla can be crater-shaped, flared, tubular, globose or urceolate. The petals are frequently fused (gamopetals), or less frequently free (polypetal). They do not have sticky substances on their surface. The calyx is persistent. Normally there are 4 or 8 stamens, it is common for them to double the number of petals, with free filaments, although sometimes they join the petals in a very basal area. They are thin, as long as the corolla. The anthers are inverted during development, so that their morphological base is atypical, usually formed by two thecas. Thecas are dehiscent by pores (poricides) at the end or by longitudinal indentations, rarely opening along their entire length. The anthers usually have spur-like modifications. Pollen is organized into tetrahedral tetrades. They may have an intrastaminal nectarific disc.

The ovary consists of 4 or 5 carpels, usually superior (hypogynous), only occasionally inferior (epigynous), and often lobed with external grooves. The placenta is primarily axillary; parietal or basal placentation is rare. There may be from one to hundreds of ovules (or seed rudiments) per locule. The ovules are anatropic, with a single tegment (unitegmic) (tenuicellate). The style is hollow and straight. They have a stigma with 5 lobules.

Bees are the predominant pollinators of heather plants, although there are others such as hummingbirds and passerine birds, some mammals and lipidopteran insects, as well as other pollinators. The shape of the flowers is adapted to the pollinators, and if similar pollinators are present in remote regions, parallel evolution can occur—that is, independent evolution in which the same changes take place. Therefore, flowers with very similar morphology may be found in distant, separate regions, but this does not necessarily mean they are more closely related phylogenetically.

Fruit, seed

The fruit is a coenocarp with 12 chambers and various types of placentas. There are three representative fruit types in the Ericaceae family: capsules with different modes of dehiscence, baccate (berry-like) fruits, and drupe-like fruits. Therefore, depending on the species, the fruit may be dry or fleshy, dehiscent or indehiscent.

Ericaceae typically have fruits with a single-layered pericarp featuring various types of trichomes and stomata; the outer region of the pericarp is parenchymatous, and the inner region is scleromatous. The pericarp of berry-like fruits consists of a single-celled outer epidermis, a hypodermis, a parenchymatous mesocarp, and a single-celled endocarp with scattered stomata. Drupe-like fruits differ from berry-like fruits in that they have a hard, multilayered endocarp.

The seeds are light brown to yellowish in color, with highly varied shapes and a thin seed coat. The embryo is slender and spindle-shaped. The seed coat consists of a single layer of cells. The seeds are small, about 1.5 mm long and 0.5 mm wide. This means they have little endosperm, which reduces their germination rate. Germination is aided by a symbiotic relationship with soil fungi.

Most species of Ericaceae are autotrophic, with fully developed seeds capable of germinating using their own reserves. There are also species known as mycoheterotrophic (subfamilies Pyrloideae and Monotropoideae). These have poorly developed seeds with very little endosperm and produce very small, globular embryos. They require the assistance of mycorrhizal fungi to complete germination. Mycoheterotrophic species are negatively affected by the presence of nitrate in the soil, whereas autotrophic species are stimulated by it or are unaffected. This may be related to the very small size of the seed and its association with mycorrhizae during germination.

Root

The roots of the ericaeae are thin, fibrous and highly branched, with very fine multicellular prolongations (100 to 170 μm thick). Epidermal cells do not form radical hairs. Most of these filaments are distributed in the surface 5 cm of the soil (they represent more than 50% of the new roots each year).

The histological organization of the root consists of a uniseriate epidermis formed by large cells, a layer of cortical parenchyma, and an endodermis with cells that have thickened and suberrated walls, Under the endodermis is the pericycle formed by one or two layers of cells, The vascular bundles in the young roots are formed by three vascular bundles, although this number may vary.

Mycorrhizae are symbiotic associations between fungi and roots. Heather plants form a special type of mycorrhiza called ericoid mycorrhiza. The fungi that form ericoid mycorrhizae are primarily ascomycetes and basidiomycetes. These fungi help extract nutrients from the soil; they can even break down organic matter in the soil by releasing enzymes, allowing for the recovery of nitrogen, sulfur, and phosphorus, as well as producing hormones such as auxin that influence the growth of the root with which they are associated. These associations allow plants to grow in poor soils. The plant, in turn, provides the fungus with organic matter obtained through photosynthesis. This symbiosis also offers advantages in soils contaminated with heavy metals and in saline soils, and it increases the plant’s resistance to pathogens.

The hyphae of these fungi’s mycelia are visible on the root surface. These hyphae produce branches that penetrate the epidermal cells and subsequently the cortical parenchyma cells, forming intracellular clusters (they are therefore endomycorrhizae). A characteristic of ericoid mycorrhizae is that the infected cells show signs of internal degradation. No hyphae are observed in the endodermis or in the vascular tissue. Some authors have found, through histological observation and molecular techniques, fungal hyphae even in the aerial parts of the plant. Initially, the fungal hyphae associate with the fine roots and then invade the epidermal cells.

Among the species of Ericaceae, there are some known as mycoheterotrophs. These plants do not perform photosynthesis, and all carbon compounds are provided by the fungus. These carbon compounds are synthesized by other plants that do produce chlorophyll. In this way, through shared mycorrhizae, carbon compounds are transferred between different plants. This type of plant has appeared in many other plant groups, so it is a trait that can evolve through convergence. There are (initial) mycoheterotrophs that act as such only during the germination period and then develop their own photosynthesis, as occurs in some species of Ericaceae (and also in orchids). There are other species that, although they perform photosynthesis, may behave as mycoheterotrophs temporarily: partial mycoheterotrophs, with the proportion of external carbon varying depending on the environment, but it can account for more than 50% of the plant’s total carbon.

Habitat, distribution

They typically live in nitrate-poor soils and can survive in soils with a pH as low as 4. They are found in the tundra, moist moors, and the understory of boreal forests in the Northern Hemisphere. Their distribution is cosmopolitan, but they are most abundant in southern Africa, North America, the Himalayas, and southeastern Europe. In Australia, there are about 371 species, more than 90% of which are endemic.

In Australia, there are phosphorus-poor regions where certain species of this family are abundant. Phosphorus can only be taken up in inorganic form, and when it is scarce, plants employ two strategies: mycorrhizae or the release of carboxylate. Species of the Ericaceae family found in these phosphorus-poor habitats are capable of releasing carboxylate to mobilize inorganic phosphorus from the soil. This strategy appears to have been acquired independently by different species, and it is not unique to the Ericaceae family.

Society

This family has many commercially valuable species, such as rhododendrons, blueberries, and strawberry trees.

Phylogeny

Taxonomy / NBCI (↗): Viridiplantae; Streptophyta; Streptophytina; Embryophyta; Tracheophyta; Euphyllophyta; Spermatophyta; Magnoliopsida; Mesangiospermae; eudicotyledons; Gunneridae; Pentapetalae; asterids; Ericales; Ericaceae.

BOLDSYSTEMS → Tracheophyta / Magnoliopsida / Ericales / Ericaceae

WFO (↗): Plantae / Pteridobiotina / Angiosperms / Ericales /Ericaceae

GBIF (↗): Plantae / Tracheophyta / Magnoliopsida / Ericales / Ericaceae

Las especies actuales de esta familia empezaron a diversificar hace unos 90 millones de años (en el cretácico tardío) desde un ancestro localizado en la región neoártica o paleoártica.

The genus Daboecia is older than Calluna and Erica, which appear to share a common ancestor.

Bibliography

Addoms RM, Mounce FC. 1931. Notes on the nutrient requirements and the histology of the cranberry (Vaccinium macrocarpon Ait.) with special reference to mycorrhiza. Plant Physiology. 6:653-668.1. DOI: 10.1104/pp.6.4.653.

Bremer K. 2003. An update of the Angiosperm Phylogeny Group classification for the orders and families of flowering plants: APG II. Botanical Journal of the Linnean Society, 2003, 141, 399–436. DOI:10.1111/boj.12385.

Figura T, Tylová E, Matsuda Y, Janoušková M, Ponert j. 2024. Nitrate inhibition of germination in Ericaceae relates to seed size and mycoheterotrophy. Functional Ecology. 39: 609-620. DOI: 10.1111/1365-2435.14710.

Kriebel R, Rose JP, Bastide P, Jolles D, Reginato M, Sytsma KJ. 2023. The evolution of Ericaceae flowers and their pollination syndromes at a global scale. America Journal of Botany. 110:e16220. DOI: /10.1002/ajb2.16220.

Kron KA, Judd WS, Stevens PF, Crayn DM, Anderberg AA, Gadek PA, Quinn CJ, Luteyn JL. 2002. Phylogenetic classification of Ericaceae: molecular and morphological evidences. The Botanical Review. 68: 335-423.

Merckx VSFT, Gomes SIF, Wang D, Verbeek C, Jacquemyn H, Zahn FE, Gebauer G, Bidartondo MI. 2024. Mycoheterotrophy in the wood-wide web. Nature Plants 10: 710–718. DOI:10.1038/s41477-024-01677-0.

Pirie MD, Oliver EGH, Bellstedt DU. 2011. A densely sampled ITS phylogeny of the Cape flagship genus Erica L. suggests numerous shifts in floral macro-morphology. Molecular Phylogenetics and Evolution. 61: 593–601. DOI: 10.1016/j.ympev.2011.06.007.

Sorokin AN, Yatsenko OV, Bobrov AVFCh, Romanov MS, Zdravchev NS, Iovlev PS, Timchenko AS, Mikhaylova AA, Vasekha ND, Kuptsov KV. 2024. The pericarp structure and histogenesis in Enkianthus: on the ancestral fruit type in Ericaceae family. Botanical Journal of the Linnean Society. 204: 76–85. DOI: 10.1093/botlinnean/boad041.

Stevens AF. 1971. A classification of the Ericaceae: subfamilies and tribes. Botanical Journal of the Linnean Society. 64: 1-53. DOI: 10.1111/j.1095-8339.1971.tb02133.x.

Villar L. 1997. Flora ibérica. Real Jardín Botánico, CSIC, Madrid. http://www.floraiberica.org/ [2024].

Wei X, Zhang W, Zulfiqar F, Zhang C, Chen J. 2022. Ericoid mycorrhizal fungi as biostimulants for improving propagation and production of ericaceous plants. Frontiers in Plant Science. 13:1027390. DOI: 10.3389/fpls.2022.1027390.

WFO (2025): Ericaceae Juss. Published on the Internet;http://www.worldfloraonline.org/taxon/wfo-7000000218. Accessed on: 10 Dec 2025

Zhou XM, Ranathunge K, Nge FJ, Liu ST, Dixon KW, Lambers H. 2025. Strategies in Ericaceae to acquire phosphorus in phosphorus-impoverished habitats in the southwest Australian biodiversity hotspot. Functional Ecology. 39: 2889-2904. DOI: 10.1111/1365-2435.70142.

Authors of images

Figura 1: Ejemplos de las 7 subfamilias que componen a la familia Ericaceae. Arbutoideae: Arbutus unedo; Cassiopoideae: Cassiope tetragona (Bjørn Christian Tørrissen: https://en.wikipedia.org/wiki/Cassiope_tetragona#/media/File:Rohkunborri-Cassiope-Tetragona.jpg); Enkianthoideae: Enkianthus campanulatus (https://commons.wikimedia.org/wiki/Category:Enkianthus#/media/File:Flowers_June_2013,_Visit_to_the_Botanics_(8999911293).jpg). Epacridoideae: Conostephium-pendulum (Geoffrey Derrin: https://en.wikipedia.org/wiki/Conostephium_pendulum#/media/File:Conostephium_pendulum.JPG). Ericoideae: Erica umbellata. Pyroloideae: Pyrola-asarifolia (Walter Siegmund (talk): https://commons.wikimedia.org/w/index.php?curid=16148956). Harrimanelloideae: Harrimanella-hypnoides (Kim Hansen: https://en.wikipedia.org/wiki/Harrimanella#/media/File:Harrimanella_hypnoides_upernavik_kujalleq_2007-07-24_2.jpg). Vaccinoideae: Agapetes-serpens (Zeynel Cebeci: https://commons.wikimedia.org/wiki/Agapetes_serpens#/media/File:Agapetes_serpens_-_Flora_und_Botanischer_Garten_K%C3%B6ln.JPG)