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Leaves of Dracontium are produced from the terminal bud on the apex of the tuber. They are solitary or sometimes more than one per tuber during vegetative reproduction. Each leaf consists of a long terete petiole with a tripartite blade held horizontally or ascending up to 45E from the petiole apex.
Petiole. The petioles of Dracontium
are thick and aerenchymatous, frequently more than 2 m and sometimes to 6
m long. The outside surface of the petiole is often highly variegated, dark
or purplish green, sometimes tinged brown, mottled with pale green or creamy
areas forming a sharp or vague reptilian pattern (
Fig. 17 ). The mottled areas often appear as upward brush strokes, which
often start at protuberances. The surface texture of the petiole is variable
among species, from more or less smooth to heavily beset with protuberances.
These are often accompanied by horizontally elongate, irregular projections
bordering two differently colored areas and sometimes also by spiny projections
to 2 mm long. The proximal half of the petiole tends to have more protuberances
or projections, while the distal half is much smoother. The aerenchyma cells
of the petiole are cylindrical, hollow, to 6 cm long and 0.5 cm wide (
Fig. 18 ). The base (sheath) of the petiole is convolute, forming a closed
space in the center, which is the site of initiation of inflorescence or leaf
(
Fig. 19-20 ).
Blades. The leaf blades of Dracontium
are papyraceous to thinly coriaceous. The upper surface is usually medium
or dark green and glossy to semiglossy or rarely matte, while the lower surface
is usually paler, and semiglossy or matte. The blade comprises a middle division
and two lateral divisions, each 0.5-1.5 m long and 0.5-1.8 m wide (
Fig. 21-23 ). Fenestrations may be present often along the rachises and
major veins (
Fig. 24 ).
The terminology of leaf blade is
explained in (
Fig. 25 ). The middle division (md) is the central division, often once
or twice trichotomously branched, yielding one terminal and two basal subdivisions.
The lateral divisions (ld) are the two mostly equal portions on opposite sides
of the middle division, each often once or twice dichotomously branched, consisting
of one terminal and one basal subdivision. The terminal subdivision (tsd)
is the central subdivision of the middle division (often consisting of one
terminal and two subterminal sections) or the basiscopic subdivision of each
lateral division (often consisting of one terminal and one subterminal section).
The basal subdivisions (bsd) are the lateral subdivisions of the middle division
or the acroscopic subdivision of each lateral division. The terminal section
(ts) is the central section of the terminal subdivision of the middle division
or the basiscopic section of the terminal subdivision of each lateral division.
The subterminal sections (sts) are the two lateral sections of the terminal
subdivision of the middle division or the acroscopic section of the terminal
subdivision of each lateral division.
The rachis (r) is the principal
axis of each blade division and may be divided into three portions: basal,
medial and terminal. The basal rachis (br) is the proximal portion, extends
from the petiole apex to the branching point of the subdivisions. The medial
rachis (mr) is the middle portion, extends from the branching point of the
subdivisions to the branching point of the sections. The medial rachis may
not exist when the terminal subdivisions consist of an entire segment and
the sections are not recognizable, as in D. angustispathum. The terminal rachis
(tr) is the distal portion, extends from the branching point of the sections
to the apex. The midribs (mdr) are the principal axes of the basal subdivisions
and subterminal sections.
The rachises of the blades may
be mottled in a pattern similar to the petioles but in much paler shades or
may be concolored, e.g., uniformly light green and sometimes tinged brown
(
Fig. 27-29 ). They are usually smooth or sometime armed with spiny projections,
also similar to those of the petiole. The basal rachis of the middle division
may be as long as (D. spruceanum) or twice or more as long as those of the
lateral divisions (D. angustispathum and D. grayumianum). The midribs and
major veins are convex and light green on the upper surface and conspicuously
round-raised and paler on the lower surface. The secondary veins are more
or less parallel and arching apically to form several collecting- veins along
the margins with the innermost being the strongest. The ultimate divisions
of the leaf are pinnately veined with a prominent network of tertiary veins.
Segments of Dracontium leaf blades
can be entire or lobed, and can be distinguished on the basis of their position.
The terminal segments of each section are called ultimate segments (us). The
segments preceding the ultimate ones back to the branching point of the sections
are called penultimate segments (pus). The medial segments (ms) are those
attached to the medial rachis. The basal segments (bs) are those attached
to the basal rachis. Sometimes, there are rounded, triangular, or oblanceolate
contrastingly small segments among the basal and medial segments. These small
segments may be absent (D. spruceanum) or alternate with the larger segments
(D. soconuscum) or more often found near the base of each leaf division (D.
polyphyllum). They may be confluent with larger segments (D. gigas) or free
(D. spruceanum). Likewise, medial and basal segments may be confluent or free
from one another.
The basal subdivisions of Dracontium
consist of many smaller segments (D. gigas and D. grayumianum) or sometimes
a single segment (D. angustispathum). The terminal subdivisions always consist
of at least two segments in the lateral division and at least three segments
in the middle division.
In the early development of Dracontium
leaf blade, all leaf divisions may point upwards (D. gigas,
Fig. 30 ; D. margaretae,
Fig. 31 , or the middle division may point up while the lateral divisions
point downwards (D. asperum,
Fig. 32 ; D. spruceanum,
Fig. 33 ). Juvenile leaves of Dracontium usually are sagittate or sagittately
lobed (
Fig. 34-36 ), rarely linear or trifid (D. margaretae,
Fig. 37 ).
