This section is from the book "Handbook Of Hardy Trees, Shrubs, And Herbaceous Plants", by W. Botting Hemsley. Also available from Amazon: Handbook of hardy trees, shrubs, and herbaceous plants.
The following Key is intended to assist in ascertaining the order to which a plant belongs. It should be observed, however, that some acquaintance with the rudiments of Descriptive Botany is necessary to enable a person to use it profitably. And it should also be borne in mind that there are many plants deficient in one or more of the characters upon which the groups or classes to which they are referred are founded. In such cases the general characters and structure of a species decide its position in a natural arrangement of plants. Of course there are differences of opinion in regard to these matters, as some botanists attach greater importance than others to the presence or absence of certain organs. In fact, some orders, as the Juglandacese and Loranthacese, are placed in different divisions by different writers. As an example of the apparently arbitrary grouping of plants, we may refer to the apetalous genera of the Ranunculaceae: Clematis, Anemone, Caltha, Helleborus, etc. Orders possessing genera wanting in any of the main characters of their division are included in the key under two or more divisions. This key is based upon that given in Lindley's 'Vegetable Kingdom,' and modified according to the scope of the present work, with the addition of habit, duration, etc., of the species.
Trees, shrubs, or herbs with more or less conspicuous unisexual or bisexual flowers and seeds containing a distinct embryo
Phenogamous Plants, 1
Trees or herbs (Ferns, Horsetails, Mosses, Seaweeds, Fungi, &c), without staminate or pistillate flowers; seeds (spores) destitute of an embryo.......Cryptogamous Plants, p. 542
Stem when perennial consisting of a central pith, concentric layers of wood, and a separable bark, increasing in size by the formation of additional layers beneath the bark, the latter expanding or renewing itself in proportion to the growth of wood. Leaves net-veined. Parts of the flower free or united, usually in fours or fives or some multiple of these numbers. Floral envelopes when present consisting of a distinct calyx and corolla, the former usually green and the latter coloured; or all the series similar, and then termed a perianth; or the sexual organs without any distinct whorl of investing organs, though sometimes subtended by bracts. Seeds with two opposite entire or divided cotyledons . Dicotyledons, 2
Stem destitute of central pith, not increasing in diameter by annual layers, vascular bundles irregularly scattered amongst the cellular tissue. Leaves usually parallel-veined (or rarely net-veined, as in the Aroidese, Smilacinese, and one or two other orders). Parts of the flower usually in threes. Floral envelopes in one or two series, free or united in some degree, usually all coloured and similar in form, sometimes reduced to scales or scaly bracts, as in Grasses and Sedges. Seeds with one cotyledon . Monocotyledons, 3
Ovules not enclosed in an ovary . Gymnosperma (Conifera and Gnetacea) p. 419-457 Petals when present free to the base or very slightly united, as in some Malvaceae.........Polypetala, p. 1
Petals usually united, forming a monopetalous corolla, or rarely almost free, as in some Ericaceae . . . Gamopetala, p. 218
Perianth usually composed of six segments in two whorls, all or some of them coloured, rarely green. Some of the plants belonging to this division have small inconspicuous flowers, destitute of a regular perianth, e.g. Aroideae, Typhaceae . . . Petaloidea, p. 458 Perianth none, or reduced to minute scales. Flowers often arranged in spikelets, and enclosed in imbricated membranous or coriaceous bracts, termed glumes. Fruits (in the orders referred to in this work) 1-celled, 1-seeded, the perianth-scales usually adhering to the fruits.....Glumifera, p. 537