Malvaceae Info (home)
I am occasionally asked to identify plants from photographs of plants, flowers or fruits. However, identification of malvaceous plants from such photographs is difficult unless the viewer is already familiar with the species, as gross morphological traits such as habit, flower colour, or leaf shape are not good guides to the taxonomic position of a plant. This page provides a guide to some traits which are more useful in pinning down an identification.
The scope of this page is restricted to the sub-family Malvoideae sensu Kubitzki and Bayer, which includes as a subgroup all the traditional Malvaceae. This includes 3 speciose groups, the hibiscuses and allies (Hibisceae), the cottons and allies (Gossypieae) and the mallows and allies (Malveae) and a number of smaller groups including Alyogyne, Lagunaria+Howittia, Radyera, Camptostemon, Uladendron and Pentaplaris.
This group is typified by the presence of monothecate stamens with bisporangiate anthers, echinate pollen, a gamosepalous calyx which is valvate in aestivation and a staminal column. The first two characters are limited use to non-specialists, being difficult to observe. The sepals (which collectively form the calyx) are fused at their base (gamosepalous) and in bud (aestivation) the edges of sepals adjoin each other to enclose the developing petals, etc (valvate); if your plant doesn't display this characteristic it's probably not in this group. The staminal column is formed by the fusion of the stamen filaments for much of their length, and encloses and adjoins the style. This is the best single character for identifying the group; however in Hoheria and allied genera, and also in Hampea and some species of Cienfuegosia, the fused section is short, and the presence of the staminal column isn't obvious to a casual examination. Furthermore it could on casual examination be confused with an androgynophore (an elongated section of the receptacle separating the stamens and styles from the petals), as found elsewhere in Malvaceae and in other taxa.
Other characters typical of the group are alternate (one leaf per node), petiolate (stalked), stipulate (with pairs of small leaf-like structures at the base of the petiole) foliage, with simple, unlobed or palmately or digitately lobed blades; an indumentum of stellate, or less commonly simple, lepidote (scale-like) or glandular hairs; and 5 unfused petals, often joined to the base of the staminal column.
The most useful characters for pinning a plant down to a particular group within Malvoideae are details of floral or fruit anatomy.
§ Many plants in the group (and elsewhere in Malvaceae) have an epicalyx or involucel, that is an additional whorl of floral parts (bracteoles or epicalyx segments) below the calyx. (An epicalyx is also found in, for example, Calystegia (Convolvulaceae).) Although the presence or absence of an epicalyx is not as significant a taxonomic trait as was thought by early botanists it is still useful for distinguishing large groups within Malvoideae (it is absent from a large clade surrounding Abutilon, Sida and Plagianthus, from most species of Sidalcea, from Napaea and some species of Callirhoe, from Palaua, from Nototriche, from Cienfuegosia, from Howittia and from a few species of Hibiscus. Care is needed for the cases where the epicalyx is lost early in floral development (as is the case in most species of Malvella), when the bracteoles are minute (as in Hibiscus schizopetalus), or when the bracteoles enclose and obscure the sepals.
When an epicalyx is present the number of bracteoles, and whether they are fused at the base or separate, are useful observations. In Uladendron, Camptostemon, Lagunaria and Calyptraemalva the epicalyx is completely fused in bud; in at least some species of Alcea it is valvate in bud. In most species of Peltaea there is not only an epicalyx at the base of the flower, but also an involucre (of bracts) surrounding a cluster of flowers. In some species of Pavonia the epicalyx is doubled (and is red, rather than the usual green).
The fruit is typically a capsule (a dry fruit with cavities containing the seeds), or a schizocarp (a fruit which is broken up into several smaller pieces). Schizocarps are found in 3 groups - all Malveae, Pavonia and allies, and Urena. The fruit is usually papery, but can be woody (as in Thespesia) or fleshy (as in Malvaviscus). The number of cavities (locules) in a capsule, or parts (mericarps) in a schizocarp is another useful observation; in flower the same number can be obtained by counting the number of lobes or branches of the style (except than in Urena and Pavonia and allies this number is twice the number of the mericarps, and in Plagianthus, Asterotrichion and some species of Lawrencia (all of which have reduced numbers of ovary locules, the number of style branches may be less reduced). The number of locules or mericarps is almost uniformly 5 in Hibisceae, but is increased in Decaschistia and Cenocentrum, and decreased in Helicteropisis, some species of Humbertiella, Kydia, Dicellostyles, Julostylis and Nayariphyton. (Some species of Talipariti and Papuodendron can have subdivided locules and can be misinterpreted as being 10-locular.) In Malveae the number is variable, usually greater than 5, sometimes much greater, but is reduced to one in Plagianthus and to a lesser degree in allied genera. It is also less than 5 in Pentaplaris, Camptostemon, and Howittia, and is 5 or fewer in Gossypieae.
The number of seeds in a locule or mericarp is another useful observation; in Kosteletzkya, Pavonia and allies, Urena, and several lineages in Malveae the locules/mericarps are uniformly single seeded. Also useful is whether a mericarp is subdivided into smaller compartments (though this can be ambiguous - I interpret the mericarps of Alcea as having a single curved locule; others describe this as 2 locules), and whether the mericarp or capsule is dehiscent (opens to release the seeds), or indehiscent (dispersed as a closed unit). In most schizocarpous genera the fruit is verticillate (mericarps arranged in a whorl), but in Malope, Kitaibelia and Palaua it is capitate (mericarps arranged in a head).
Staminodes (sterile, often petaloid, stamens) are widely present in Malvaceae. In Hibisceae and Gossypieae they number 5, and are reduced to either 5 teeth at the top of the staminal column, or to an extension of the staminal column beyond the departure of the last filament. In Malveae they are lacking, except in Neobaclea. They are also lacking in Alyogyne.
Whether the style is lobed or branched is a useful observation, and so is the number of lobes of branches. So is the shape of the stigmas. The stigmas are typically capitate (spherical) but can be capitellate (small sphere), clavate (club-shaped), peltate (disc-shaped), or filiform. Filiform stigmas characterize the Eurasian Malveae (Malva, Lavatera, Malope, Kitaibelia, Alcea and Althaea), Sidalcea, Callirhoe and Napaea, and some species of Anisodontea. In Plagianthus and allied genera the stigmas can be capitate, clavate or filiform.
In most genera the flowers are hermaphrodite, i.e. bear both functional stamens and styles. (Note, however, that many are protandrous, i.e. the stamens develop before the styles, which can mislead.) In a few genera separate male and female flowers are borne. (Note that non-functional reduced stamens and styles are often present.) Genera with separate male and female (unisexual flowers) include Hampea (excluding H. rosavirae), Plagianthus, Asterotrichion, Gynatrix and some species of Lawrencia, and Napaea. Cienfuegosia rosei and some species in Callirhoe, Eremalche and Sidalcea have separate female and hermaphrodite flowers.
Finally there are some unusual features that characterize small groups, such as the phyllanthophory (partially fused leaf and flower stalks) of Nototriche and some species of Tarasa, the laciniate petals of Hibiscus schizopetalus, the unusual calyx and corolla shape of Abutilon megapotamicum, and the deciduous spathaceous calyx of Abelmoschus.
Features which are useful once the position of a plant has been narrowed down are petal colour (typically yellow, or pink or red to purple, more rarely orange, blue (Howittia, Corynabutilon, some Alyogyne) or white); petal shape, such as whether emarginate (lobed), truncate, erose (toothed) or rounded at the apex, or auriculate or not at the base; sepal and bracteole colour, when other than green; the shape of the leaves; when the plant is heterophyllous (has variable leaves) then the pattern of the variation depending on season or position; the presence and location of nectaries; and the nature and distribution of hairs.
© 2004, 2004, 2006 Stewart R. Hinsley