Key to Tasmanian Dicots

These six groups are usually immediately recognisable but each is so large and variable that it is difficult to write a sensible key to discriminate them. However these notes will help identify which group any particular plant belongs to. A note for more taxonomically minded readers: as a matter of convenience, I have used old-fashioned definitions of monocots and dicots: Hydatellaceae are included as monocots, and Atherospermataceae, Lauraceae and Winteraceae are included as dicots, even though none of these families is closely related to the true monocots and eudicots.

The mosses and liverworts are all small (sometimes very small) plants which do not produce flowers. The key features of liverworts are that they are either thallose (lacking leaves, instead with flat layers of tissue for photosynthesis) or leafy, with leaves arranged in two or three rows. The leaves do not have true midribs (although a few genera, including Bazzania, have a differentiated band of cells in the mid lamina), and are often lobed or with distinct teeth. The capsules are short lived, with slender stalks. They open longitudinally.

The mosses have leaves but are often a little more robust than leafy liverworts. The leaves are unlobed (but Fissidens species have a large wing on the back of the midrib), often have midribs, and are usually spirally arranged, less commonly in four or five rows, only occasionally in three rows (e.g. Cyathophorum). The capsules are typically robust, and often persist for months. The capsules of most mosses have a cap on top that is shed to allow the capsule to open.

Most ferns and fern allies (a grab bag term that, in Tasmania, includes the lycopods and Tmesipteris) are usually obvious. In difficult cases, key points are that they produce spores (and not pollen or seeds), either on the underside of the leaves (most ferns), in cones (many lycopods) or in or near the axils of the leaves (Tmesipteris, Isoetes, Huperzia and Selaginella). Aquatics may be confusing (Marsilea has clover-like leaves, Isoetes can look a little like a tufted grass or rush, Azolla could be confused with a pond-weed).

Conifers are always trees or shrubs, almost all monocots are herbs (exceptions in Tasmania Xanthorrhoea and Cordyline; also palms), dicots can be either woody or herbaceous. The reproductive structures of conifers  lack petals and sepals, and often form cones. The monocots and dicots often have showy flowers with sepals and coloured petals, although a few species produce cones that can resemble conifer cones (Allocasuarina). Conifers always have distinct male and female cones, but a high proportion of dicot and monocot species have flowers with both male and female flowers.

The conifers have single-veined leaves that are often scale-like, although in Phyllocladus these have been fused into broad, flattened photosynthetic stems, and in Podocarpus, the leaves are flat and can be up to 3-4mm wide, but the leaves of all the other conifers are less than 1mm wide.

The dicots and monocots have leaves with many veins (although this may be hard to see). Some dicots and monocots have scale like leaves (e.g. Allocasuarina, Santalaceae, Asparagus).

Grass-like leaves and growth habits usually say “monocot”. A few dicots have this habit (e.g. Stylidium, Limosella). Zantedeschia is a monocot with dicot-like leaves.

Most monocots have leaves with parallel venation (i.e. the main veins in the leaves arise right at the leaf base and run parallel along the leaf). The main exception is Zantedeschia). Only a few dicots do (e.g. many Tasmanian Ericaceae, some Myrtaceae,  some Plantago).

Lobed leaves, or leaves with teeth with veins leading to them are common in dicots, but do not occur in conifers (but see Phyllocladus) or Tasmanian monocots.

The number of petals and sepals can help discriminate between monocots and dicots. Monocots usually have multiples of 2 or 3, dicots usually have multiples of 4 or 5.

© 2011 University of Tasmania