Malvaceae (Mallow Family) s.s.

Above: Malva sylvestris. The family Malvaceae can be defined in the broad sense (sensu lato) to include the Malvaceae (e.g. Malva, Okra, Hollyhock, Gossypium (source of cotton)), Tiliaceae (e.g. Lime Tree, Tilia), Bombacoideae (e.g. Baobab), the Helicteroideae (e,g, Durio) and the Sterculioideae (e.g. Cola) and a few other 'families' as sub-families. However, when defined in the strict/narrow sense (sensu stricto) the family Malvaceae includes only those plants traditionally classified in the family https://monoecious.wordpress.com/malvaceae-s-l/. Here we stick with the strict sense, since these plants have more similar morphologies.

Above and below Malva sylvestris (known as Common Mallow in Europe). Typical of Malva the calyx consists of fused sepals with 5 sepal lobes and an epicalyx (whorl of bracts beneath the sepals) of three separate leaves. The epicalyx is derived from bracts or bracteoles (secondary bracts associated with the individual flower stalk or pedicel, whereas primary bracts are associated with the inflorescence stalk or peduncle) suggesting extensive shortening of the pedicel. The flowers are bore on an irregular raceme (a central axis bearing flowers on stalks) or axillary cyme according to some sources, with several peduncles arising from each node.

The five petals are pale purple, each with 3 to 5 dark veins that unite at the base and a loved apex. The thickened bases of the petals are fused together and are also mucilaginous: releasing mucilage if wounded. Some variants have white flowers with pale purplish veins). A tube of an indefinite number of fused stamen filaments (a monoadelphous androecium) borne on the petals, surrounds the carpels and style. Each anther is monothecous, containing just one pair of pollen sacs (though the anther stalks break away from the column in pairs with a common filament, so the original anther may be dithecous). The carpels are fused into a torus with one ovum per carpel. There are at least 10 carpels. The single style branches into numerous (10 or more, presumably one per carpel) elongated stigmas.

Mallows are pollinated by a variety of bees. In Malva sylvestris the nectary consists of secretory hairs on the margins of the petal bases, the hairs on one petal margin interlocking with those from the adjacent petal. The stiffened petal bases are inserted below the superior ovary. The petals form a landing platform for the bees who will pick up or deposit pollen when reaching the nectary.

The flower above is clearly in the male stage (notice the pollen on the petals). Malva flowers are protandrous: the male organs ripen first, followed by the female organs. This helps increase the likelihood of cross-pollination. The flower below is entering the female stage: most of the ten (or more) stigma filaments have emerged.

The white regions in between the petals at their bases are the nectaries: fields of interlocking hairs extending from the margin of each petal claw (the claw is the narrowed stalk-like basal part of a petal in a clawed flower).

Pollination mechanism. The claws of the petals near to the nectaries collect pollen from the anthers, which evidently gets caught by short hairs on the inner surface of the claw. Some pollen also remains for a time on the dehisced anthers and the short hairs on the stamen filament tube may also trap shed pollen. A bee landing on the petals and reaching the nectaries will likely come into contact with this pollen and pick some of it up. When the flower enters the female stage, the style elongates and the long stigmas emerge from the stamen tube to pick up pollen from a visiting insect.

Above: top of the staminal tube, showing the dehisced anthers with clumps of beautiful pearl-white pollen grains still attached. Note that although each anther only has one lobe (it is monothecous) with two compartments for pollen (it has two pollen sacs and is said to be bisporangiate) the anthers emerge in pairs from common stalks. The anthers of most plants have two lobes, they are dithecous, with two pollen sacs per lobe: they are terasporangiate. In Malva the two lobes have apparently become separated on stalks that branch from the stamen filament. The pollen of Malva sylvestris is quite large (about 110 μm diameter). They are also covered with small spines (hard to see here as my mobile phone lacked the necessary resolution, but they can be seen on the magnified image below and were beautifully clear down the microscope).

The spines on the pollen are of two types in Malva sylvestris: long, slender and pointed; short and rounded (see:  Christensen, P.B. 1986. Pollen morphological studies in the Malvacea. https://doi.org/10.1080/00173138609428890). These spines function to help the pollen attach to a visiting insect, and the pollen is indeed very adhesive.

Above: looking down on the anthers. the yellow pollen, which comes in very different sizes, is probably pollen deposited by a visiting insect (or by wind) from other species (I have found no mention of more than one pollen type being produced in this species).

Above:pollen caught on the inside of a petal claw. This region of the petal is covered in short hairs (some of which are visible here) which seem to help trap the pollen, although the pollen is intrinsically adhesive.

Above:the stamen tube has been slit to reveal the long stigmas within. there were 10 of these strap-like stigmas, which were unbranched and covered in minute hairs which presumably help pollen to stick to their receptive surfaces. This flower was clearly in its male stage and eventually the style would have elongated and the stigmas would have emerged and spread apart.

Note: Malva sylvestris is common in the area of study - if you want to study flower structure then only pick what you need and avoid collecting material from designated nature reserves (unless you have explicit permission to do so) and know the local laws regarding what can and can't be picked. Avoid picking materials from an area where they are infrequent or rare. This not only protects the plants but also leaves them for others to enjoy. In this study satisfactory answers on the floral structure could not be found from the available literature so it was necessary to dissect a flower and a single flower was quite sufficient to answer the questions raised.

The leaves, fruit and flowers of Malva sylvestris are edible and the leaves can be cooked to make a mucilaginous porridge. 'Malva' means 'soft' and some say this alludes to the mucilaginous nature of these plants. Marshmallow confectionery was in the past made mainly from Althaea officinalis, another member of the Malvaceae.

Above:an upright specimen. Note the twisted folding of the petals in bud. The stems of Malva sylvestris are ascending (lying down but erect at the tips) or decumbent (prostrate, i.e. lying horizontal along the ground). The leaves (except for the lowest) consist of 5 or 7 shallow lobes of which the middle lobe is the longest. The lower 'root' leaves are roundish with cordate (heart-shaped) bases and with very shallow lobes and may have a purple blotch at their base (below). The cauline (stem) leaves become smaller, more shortly stalked and more deeply lobed towards the shoot apex and the central lobe becomes more prominent. The stems are numerous and 2 to 3 feet (60 to 90 cm) in length/height.

Malva sylvestris is a perennial or annual and occurs along roadsides and in waste places and prefers damp places, such as near the sea, near to marshes, in ditches, and along river banks, especially tidal river banks. most of the specimens photographed here were found near It is native to southern Europe, northern Africa and southwestern Asia, but has been introduced and naturalized over much of the globe.

Above: the fruit of Malva sylvestris. The fruit is a schizocarp: a fruit that splits apart into its constituent mericarps. Each mericarp contains a single seed. The fruit is a torus made up of segmental mericarps, rather like the sectors of an orange in arrangement or like wedges of cheese, hence the alternative common name of this plant as 'cheese flower'. The torus of mericarps The fruit are edible and reportedly have a nutty flavor. Note that the sepals remain in place to cup the fruit. Be careful counting the mericarps: each has a groove in the middle which extends a certain distance back, so what looks like two mericarps may in fact be one. (Based on a photograph: https://www.flickr.com/photos/fturmog/1402925498). the texture of the mericarp surface is an aid to identifying different species of Malva.

Above and below: the fruit of Malva sylvestris.The brown-olive fruit have a honeycomb texture on the back of each mericarp (smooth but roughly hairy in Malva moschata). The fruit-bearing peduncles spread outwards (they are erect in Malva moschata).

Above: the fruit of Malva neglecta (based on a photograph: https://www.karengoatkeeper.com/2017/common-mallow-malva-neglecta/).

Above:a diagrammatic section through the ovary of Malva sylvestris, with two component carpels, each with an ovule inside. The ovules have axial placentation, meaning that each is connected to a placenta attached to the central axis of the torus (each placenta attaches to the inside of the carpel wall, the carpel being a modified leaf). The developing ovule receives nutrients through the placenta.

Above: the ovary of Malva sylvestris with the stylopodium (foot of the style) still attached.

Above: Malva sylvestris.

Malva neglecta (Dwarf Mallow)

Above: Malva neglecta (Dwarf Mallow) is a striking prostrate annual herb with roundish or kidney-shaped lobed leaves and smaller flowers with whitish petals with lilac veins. It is found on beaches (as here) and on waste ground and roadsides.

Malva moschata (Musk Mallow)

Above: the Musk Mallow (Malva moschata) which is said to have a faint musky odor. The very deeply divided palmate leaves in the background belong to this plant and are a diagnostic feature. other diagnostic features are: the usual pale pink color of the flowers (sometimes white) which have noticeably emarginate petals (the apices of the petals lack definite margins and usually look ragged, however the term 'emarginate' refers to the notch at each petal apex).

Musk Mallow has erect stems (rather than decumbent / ascending as in Common Mallow) and the leaves (except the lowest) are tripartite with deeply cleft segments and pinnatifid (pinnatifid: clefts reaching at least half-way to the midrib). The lower leaves are reniform (kidney-shaped) and 3-cleft, upper leaves more divided with shorter stalks and a pair of small lanceolate (lance-shaped) stipules. (Stipules are small lobes of leaf tissue either on the leaf-stalk or at its base and the leaves of many plants have them; they are part of the leaf rather than separate bracts). It is found on hedgebanks and the borders of fields.

The rootstock puts out several stems up to 3 feet (90 cm) tall that are frequently purple-spotted. the flowers close at night.

Malva pulsilla (Malva rotundifolia) (Dwarf Mallow)

The central stem is erect and surrounded by spreading decumbent/ascending stems with leaves only slightly smaller towards the apex. The whitish petals are tinged lilac towards the apex and have 3 or 5 lilac veins united at the base.

Lavatera arborea (Tree-Mallow)

Above: Tree Mallow (Malva arborea = Lavatera arborea) is a biennial found on maritime rocks and coasts in the south and west of Britain, and occurs naturally in southern and western Europe and North Africa, and has been introduced to other regions, such as the western coast of the United States.

The stem is erect, stout and woody (and surprisingly well-developed for a biennial - some sources state it is perennial). The upper leaves have five lobes and have a velvety texture.

The Smaller Tree Mallow or Cornish Mallow (Lavatera cretica = Malva multiflora) has been well studied for its suntracking or diaheliotropic leaf movements in which the leaf blade tracks the Sun across the sky to maintain itself perpendicular to the Sun's rays for maximum light interception. Leaf movements have been noted in other related species, such as Malva neglecta (Dwarf Mallow), Malva parviflora (Little Mallow) and Malva verticillata (Chinese Mallow).

Sleep movements (nyctinasty) in which the leaves rise up at night have also been recorded in Malva. Whether such leaf movements occur in Malva sylvestris and Malva arborea is not apparently documented, so there is an opportunity here for those prepared to make patient observations. However, the flowers of Malva sylvestris can be seen to close in the evening.

Above and below: Fruit of the Tree Mallow. Note the 3 prominent and characteristic bracts behind the fruit.

Below: fruit of Common Mallow (Malva sylvestris) - note the orange / rust-colored bulges - these are masses of the rust fungus Puccinia malvacearum or Hollyhook Rust which is a basidiomycete. This fungus attacks both Hollyhock (Althaea) and Common Mallow.

The rust-colored masses are bundles of spore-bearing hyphae (cellular threads) erupting through the epidermis of the sepals and leaves. These are sometimes called 'pustules' but this term suggests they consist of infected host tissue when really they are fungal masses so a different term would be preferable.

Rust fungi are basidiomycetes and hence relatives of the edible mushroom, though clearly greatly modified for their parasitic existence. They can have complex life-cycles, sometimes alternating between two different hosts and producing sexual spores and a variety of asexual spores.

Article created: 21 Sep 2020

Article updated: 16 July 2022.