The Petiole - Critical revision of the genus eucalyptus Volume 6: Parts 51-60
a. Its presence.
Once more we have to deal with variables. For example, it is probable that in
some cases quoted the record “Slightly petiolate” will, with further experience, turn
out to be “Sessile.” The tendency is for the records of petioles to indicate
diminished length in juvenile leaves as we get to know more about them, and, as
regards the truly petiolate ones, for us to find that the petioles become increased in
length. In some cases, the same species may appear in more than one list.
We, therefore, in this particular enumeration, can only take cognisance of those
juvenile leaves which are—
1. Slightly petiolate.
3. Petiolate very long, and, as an exceptional case,
1. SLIGHTLY PETIOLATE.
E. de Beuzevillei.
E. calycogona var. gracilis. E. Guilfoylei.
E. Le Souefi.
E. de Beuzevillei.
E. pyriformis var. Kingsmilli.
3. PETIOLE VERY LONG.
4. PELTATE LEAF.
A very few at that age (what Bentham calls “sapling leaves”) especially in the
Corymbosae series, appear to be already alternate, but have the lamina peltately
inserted on the petiole above the base, but our data on that point are but very scanty.
(B.Fl. iii, 187.)
The petiole is a continuation of the midrib, and in peltate leaves the base of the
leaf is extended below the point of insertion of the petiole into the leaf.
The remarks of Mueller in “Eucalyptographia” on the peltate leaf are chiefly
based on E. peltata, a species which, at Part XLII, p. 33, I have shown to have been
erroneously understood by him as regards its mature leaves. Bentham followed
Mueller's earlier description of E. peltata as regards the supposed peltateness of the
Then Naudin has some remarks on the subject, translated herewith:—
. . . These are not the only modifications of the foliage in Eucalyptus. There are
some species in the group, which in opposition to the preceding can be called
reason of the insertion of the petiole at a certain distance from the base of the leaf.
E. gomphocephala. E. saligna.
E. Le Souefii.
E. Hillii (very).
E. Foelscheana. E. populifolia.
This character is not very constant, for in the same species one finds species which
have it and other which have not. Besides, it does not generally affect more than the
first five or six first leaves, sometimes also a large number. But if it is transitory in
these species, it becomes permanent in others; it is at least the case of E. peltata,
whose leaves remain peltate during the whole life of the tree. (Naudin, 1st Mem.,
A few years later, Naudin wrote:—
There is finally a last peculiarity, the way in which the petiole is inserted on the
blade. In the great majority of species this insertion takes place at the very base of
the blade, as in our native (French) trees, but there is a small number of them in
which it occurs a little below the insertion of the petiole. The result is what is called
peltate leaves. This modification is always limited to the juvenile stage, except in
one species, E. peltata, in which this character becomes permanent. (Naudin, ii,
In ii, 16, Naudin adds citriodora, maculata, and calophylla as having peltate
leaves. He is referring to very young leaves. No species has peltate leaves
throughout the whole life of the species; the mistake, as regards E. peltata,
originated with Mueller, and has already been dealt with.
So far as I have seen, the peltate leaves preponderatingly belong to the
Corymbosae. Those that I have seen are, and no doubt peltateness will be found in
In addition, we have E. erythrocorys (belonging to the allied Eudesmieae), and
others should be searched for.
2.Stem-clasping, i.e., with expansions of the lobes of the leaf.
2a. Stem-clasping and crowded.
It will be seen at once, on examination of a sessile leaf, say E. Gunnii, fig. 6a,
Plate 108, Part XXVI, that the bases of the two leaves touch the stem.
It must be understood that, in dealing with juvenile leaves, their insertion on the
E. calophylla. E. peltata.
(a) Petiole (or absence of it).
(b) The common axis or stem, not the petiole.
The following leaves are sessile, or practically so:—
In other words, we have basal expansions of the lobes of the leaves. The bases, in
connection with an appropriate shape of the leaf, gives us a cordate leaf, and the
stem-clasping leaf itself is often termed amplexicaul. At p. 291, under “Shape,” they
are separately classified under broad and narrow. In the list which follows, those
inclined to be narrow are indicated by (N).
E. angophoroides. E. odorata.
E. dichromophloia. E. resinifera.
E. macrorrhyncha. E. vitrea.
E. angophoroides. E. Muelleri.
E. Benthami (N).
E. de Beuzevillei.
E. nitens (N).
2a. STEM-CLASPING AND CROWDED.
This sub-head may prove convenient for purposes of rough classification.
Connate or Perfoliate.
This is a question of fusion of two leaves by their bases, around a common axis or
stem, not petiole.
It even happens in a small number of Eucalypts, that these opposite (i.e., sessile
and opposite during a long period of the youth of the tree) leaves unite by their base
and become what is called connate, forming then a single piece, which is traversed
through its centre by the stem or the branch. This new disposition of the foliage is
sometimes transitory, as in E. Risdoni, sometimes permanent as in E. gamophylla,
The concrescence of the leaves by pairs in all stages of growth occurs, so far as
known, only in E. perfoliata, if even in that rare and little known congener this
coalescence should prove also exceptional.
If Plate 180, Part XLIV of the present work be referred to, it will be seen that this
species is not perfoliate throughout life.
Besides those species mentioned by Naudin as showing perfoliation, we may
include E. pulverulenta, E. Perriniana. A figure of a perfoliate leaf (E. Perriniana)
may be seen at fig. 11, Plate 83, Part XIX (erroneously as E. cordata).
See fig. 1a, Plate 32, Part VI, for the connate leaves of E. Risdoni encircling the
stem. This particular twig shows flowers and fruits, the leaves still exhibiting
juvenility. Perfoliate leaves of E. gamophylla will be found figured on Plate 147,
Scars on branches and trunks.—As growth proceeds, the rachises increase in
diameter, and stretch the bases of the perfoliate leaves. The leaves are persistent for
a long time, and leave circular ragged scars or fragments on the branches and on the
main trunk, even when the latter attain several inches in diameter. This character
seems rare in Eucalyptus. I have seen it in E. pulverulenta (see Part XXI, p. 15), but
only in a very marked manner in E. Perriniana. It, however, probably occurs in all
Fusion of leaves by margins.
We have already spoken of fusion of leaves by their bases, but we may have
fusion taking place at other parts of their margins.
This is an unusual occurrence in Eucalypts; the following are the only cases
known to me. Additional instances should be searched for:—
1. E. numerosa, Bega district (James Taylor, May, 1918).
2. E. maculosa, Blackheath (R. H. Cambage).
3. E. cordata. In specimens growing in the Botanic Gardens, Sydney, the laminae
are sometimes fused both basally and laterally.
At Part XLIX, p. 279, we have already spoken of Cohesion of Branches. This
fusion may be referred to as “Cohesion of Leaves.”
Decurrence of Leaf.
When the green tissues of sessile leaf blades is continued down the stem, by
adhesion, in the form of two green bands or wings, the leaf is said to be decurrent.
A marked case is rare in Eucalyptus. We have it in E. Flocktonioe, figs. 3a to 3c,
Plate 236, Part LVIII, which is the best example known to me. It occurs also in E.
macrocarpa, fig. 1a. Plate 77, Part XVIII.
The typical form is morphologically close to “stem-clasping,” and less close to
that extreme form of quadrangularity which exhibits that type of winged stem which
is familiar to us in E. quadrangulata and E. tetragona. In the latter species it is not
the lobes of the leaf (or of two opposite leaves) which are concerned, but one (or
two) flattened or expanded petioles, with no lamina.
Angularity of Branchlets.
A few notes may be required on some of the minor characters which I have made
use of or neglected in the specific diagnosis and descriptions. I have thought it
generally useless to describe the branchlets terete or angular, for in those species
such as E. pruinosa, E. tetragona, E. tetraptera, &c., where the angles are often so
prominent as to be almost transformed into wings, there occur branches, often on
the same specimen, quite terete. (B.Fl. iii, 186.)
For sketches of angular stems of these species, see E. pruinosa (Part XII, Plate
54); E. tetragona (Part XLVI, Plate 188); E. tetraptera (Part XXII, Plate 94). An
exaggerated case is that of E. quadrangulata, of which a section of the young stem
is figured at fig. 4e, Plate 103, Part XXIV.
It is probably the case that some branchlets will be found to be angular in all
species. The following are some in which I have personally observed to be marked,
in addition to those mentioned by Bentham, and I could mention others.
E. globulus and its allies.—E. Maideni, E. unialata, and E. goniocalyx.
E. tereticornis and its allies.—E. rostrata and E. amplifolia.
In a note “On the forms of Stems of Plants” (British Association Meeting, 22nd
August, 1904), Lord Avebury remarks: “Plants with quadrangular stems always
have opposite leaves.” He was referring to such families as the Labiatae, but it is
true of many Eucalypts, so far as the juvenile foliage is concerned.
Their texture is very variable. In all the species there is a certain firmness, but
with some, this firmness makes them exceptionally coriaceous. (Naudin, 2nd Mem.,
Mr. R. H. Cambage is one of the few botanists who has written on the subject:—
The thickening of the epidermis for the purpose of sheltering the stomata, is one of
the expedients resorted to by the Eucalypts to resist evaporation, and consequently it
E. cosmophylla. E. Planchoniana.
E. Kybeanensis. E. propinqua.
E. macrocarpa. E. punctata.
is compatible with such an endeavour, that those species having the thickest
epidermis and of which such as E. dumosa may be taken as a type, are commonest
in the interior. But this particular character is to be met with intermittently in all the
four climatic divisions of New South Wales, so that it would appear that various
species have adopted this precaution for preservative objects but from different
causes. A dwarfed Port Jackson form of E. capitellata has remarkably thick almost
orbicular leaves, while large normal type specimens within a few miles have
lanceolate foliage of ordinary thickness. The thick-leaved form, however, grows in
the more exposed positions, and in the more rocky situations with probably less
plant-food available. It seems therefore not improbable that in order to counteract
the effect of strong winds, to which its exposure renders it liable, and also to
compensate in some way for the limited nourishment it obtains, that the thick-leaved
adaptation has been evolved in this case, to preserve the starch which forms in the
leaf and which is regarded as an auxiliary food supply. It is of interest to note that
the thickest leaved types usually correspond with the more dwarfed forms, and
when the same species at maturity occurs both as large and as stunted trees, it is on
the latter that the thickest leaves are found.
Turning next to the Eucalypts in the cold climate, we find a similar variation in
leaf characters. The foliage of E. Gunnii as dwarfed trees on Mount Roland in
Tasmania at nearly 4,000 feet above sea-level, is distinctly thicker in texture than
that of the same species around Guildford Junction at an altitude of 2,000 feet, and
where the trees are upwards of 80 feet high.
The leaves of E. coriacea are always somewhat leathery, as the specific name
would imply, but in observing trees of this species from just above the 2,000-feet
level around Goulburn upwards to the 6,000 feet level towards Kosciusko, it is
found that with the ascent the leaves get gradually smaller and thicker, and the trees
become dwarfed from the rigid conditions and weight of winter snow, until at last
they appear as gnarled shrubs with interlacing branches and the now thickened
leaves have been reduced in length from about 6 to 3 inches.
It therefore appears that the sub-arid conditions of the inland country, and the
coldest effects of the mountains, though extreme in their climatic influence, have so
operated in regard to this particular phase of leaf character as to bring about the
same result. It is suggested, however, that the modifications of the internal structure
of the leaves of two Eucalypts which originated before the Kosciusko uplift, and
developed until the present time under those two extremes of climatic influence,
would not be the same, and, although the leaves of E. coriacea at 6,000 feet have
their counterpart in the interior at 500 feet, so far as the thickening character is
concerned, yet in their venation they are distinct from those of all species found in
that dry region. (Proc. Roy. Soc. N.S.W., xlvii, 36, 1913.)
I quite agree with Mr. Cambage that thickness in leaves is sometimes evidence of
lack of transpiration. The thickest leaf in Eucalyptus known to me is E. tetraptera
(and to a less extent E. Preissiana). Both of these are denizens of a coastal region in
south-western Australia, east of a well-watered belt. The saline winds (tending to
xerophytic conditions) and a moderate rainfall, combine to induce this thickness of
tissue. E. incrassata var. angulosa, very common near the sea in Western and South
Australia, may be even succulent in texture. To mention other species which love
the saline breezes would be to enumerate those with abnormally thick leaves. Thus
we have E. capitellata, E. obtusiflora, and many others.
Cold localities (e.g., mountain-tops) also check transpiration and induce thickness;
thus we have E. coriacea, E. alpina, E. coccifera, E. Gunnii. (These are the species
that are included in a list of those that cattle eat in droughty times, but it must be
borne in mind that they frequent localities not subject to great droughts. See my
“Forest Flora of New South Wales,” Part LXX, p. 445.)
Conversely, we have thin leaves to facilitate transpiration, such leaves being
always denizens of brushes, most commonly on the east coast, where the dense
growth of the rain forests induces shelter. Very thin leaves, usually with pale
undersides, can be found in such species as E. microcorys, E. acmenioides, E.
accentuated in the juvenile foliage. These thin leaves tend to be horizontal. See pp.
288 and 324.
It is obvious that, since the texture of a leaf varies according to the ecological
conditions of the plant, there is much variation in the records of this character.
The following grouping of leaves under varying degrees of thickness has a basis
of truth in it, but must be studied in a truly philosophic spirit. These lists (as indeed
all under Juvenile leaves) are based on examination of actual specimens).
E. elaeophora (sometimes).
E. de Beuzevillei.
E. Dalrympleana. E. linearis.
E. Parramattensis. E. Smithii.
E. angophoroides. E. neglecta.
Somewhat Thick or Thickish.
E. gomphocephala. E. Staigeriana.
E. angustissima. E. longicornis.
E. approximans. E. Normantonensis.
E. drepanophylla. E. spathulata.
E. Drummondii. E. squamosa.
E. erythrocorys. E. Stricklandi.