A-Z of botany: Monocotyledon
Flowering plants are generally neatly divided into Monocotyledons and Dicotyledons, based upon the number of seed leaves. This is not quite up to date, nor will some of the following comments be, but then it all gets too complicated. Conveniently, you do not have to actually see the seed leaves to tell if a plant is a monocot’ or a dicot’. As a general rule, not only do monocots have one seed leaf but their leaves are linear and narrow, the veins are parallel in the leaf and the flowers have parts in ones or threes. This contrasts with dicots which have two seed leaves (though they sometimes remain below the soil after germination), branching veins on the generally broad leaves and the flowers usually have parts in fours and fives.
In our temperate gardens, apart from the grasses (Poaceae – previously Graminae), the three main monocot families are Iridaceae, Liliaceae and Amaryllidaceae. Many monocots, but not all, produce bulbs or corms. Bulbs and corms are not produced by dicots – though these may form tubers. In general, monocots do not produce woody stems and are herbaceous but there are notable exceptions such as bamboos (woody grasses) and palms. Cordylines are well known and woody too and in the Asparagaceae.
The Iridaceae have three outer petals (better called tepals since there is no clear difference between the three outer and three inner floral parts) and three inner tepals. The ovary (seed pod) is below (or outside) the flower and the stigma is usually three-lobed. Most distinctively, there are three stamens. So although crocosmias, freesias and iris do not look obviously similar, they are in Iridaceae because they share the same number of stamens. So do crocus, gladioli, tigridias and, of course, iris.
The lily family, Liliaceae, is something of a problem these days since it has been split up into lots of smaller families such as Hyacinthaeae and Colchicaceae. But, ignoring this and taking the group as a whole, the old Liliaceae have the same three and three tepals but six stamens and the ovary is within the flower (superior ovary).
The Liliaceae contains tulips, lilies, erythroniums and fritillarias. Other plants that used to be included are:
Allium, agapanthus, tulbaghia and Ipheion – now Alliaceae
Eremurus and kniphofia – now Asphodelaceae
Colchicum and Gloriosa – now Colchicaceae
Albuca, chionodoxa, muscari, camassia, scilla and hyacinth – now Hyacinthaceae
And lastly the Amaryllidaceae which have three outer and three inner tepals and six stamens but the ovary is behind or below the flower (inferior ovary). Apart from the common houseplant amaryllis (actually hippeastrum) the best known is the humble daffodil.
Of course this is a bit complicated by the fact that the daffodil (narcissus) have a corona, made of extensions of the stamens which looks like extra petals.
The family includes many familiar garden plants including nerine, crinum and galanthus.
But there are other monocot families. These include palms and Orchidaceae.
There are always exceptions to the rules and the Araceae don’t fit the foliage plan of monocots, they are usually broad and not narrow at all. The ‘flowers’ are odd too, with a leafy spathe surrounding the spadix that carries the true flowers. But the male flowers (there are separate male and female flowers) often have six stamens, though there may be only one. It is a huge family that includes the useful Arum italicum (below).
And the vigorous climber Monstera deliciosa.
And here are some dicotyledons – tomato seedlings.
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