Three forms of Chaptalia texana

Type IType IIType III
[Click to enlarge.]

Chaptalia texana — Three Types

by Bob Harms email-here

The heads of C. texana consist of 3 series of flowers (thus trimorphic):

a peripheral series of ligulate (ray-like) pistillate flowers (which may be greately reduced^* or even missing — heads lacking this series are bimorphic)
^*Reduction of the peripheral florets in the populations studied ranged from short, erect ligules, extending only slightly above the phyllaries (Type II) to vestigial ligules shorter than the style branch point (Type III) to eligulate florets with tubular corollas longer than half the length of the style (Type IV & fall-to-winter heads of all populations). Only a few heads during the fall period were found to be truly bimorphic.
Two specimens among the 40 Texas specimens in the TEX/LL herbaria appear to be bimorphic, but without carefully dissecting the entire head (as was done with the fresh specimens studied), it is not possible to determine whether these are truly bimorphic.
a central group of perfect flowers (similar to disc flowers)
an intermediate (large) group of eligulate pistillate flowers with tubular corollas (not more than than half the length of the style)

Additionally, our Chaptalia populations studied exhibit the seasonal head dimorphism observed by Nesom for the genus Leibnitzia (FNA) (which has never been noted for Chaptalia):

The species are characterized by dimorphic heads: those produced in the spring appear before or with the leaves and are chasmogamous and quasi-radiate; the fall forms appear after the leaves and are cleistogamous (not exposing any florets but setting full fruit).^*
^*Although the details of the dimorphism described by Nesom only apply to Type I, the fall/winter heads of Types II & III are either bimorphic or exhibit peripheral florets without ligules.

I have long been familiar with the nodding closed heads of C. texana in the hill country west of Austin, Texas, but in mid March of 2010 I came across a population with an erect open head with ray-like ligulate florets (Type I in this presentation). The Texas Chaptalia literature did not seem to fully account for either this new type or the more familiar type. The Chaptalia authority Guy Nesom has encouraged me to pursue this issue further, so I have done my best to provide detailed descriptions of the various types that were available to me from spring 2010 through January 2011.

Before proceding with own collections I examined all C. texana Texas specimens in the TEX/LL herbaria. But in light of what I found with the fresh materials, I was obliged to visit the herbarium specimens yet several more times, each time discovering features missed in my initial inspection.

Especially upon closer examination of the closed head forms I realized that I had not fully appreciated their diversity of floret structure, and I was able to identify two distinct larger populations in N. Hays County: one with small ligules, visible at anthesis (type II); and one with vestigial ligules, often difficult to discern even with a microscope (type III). Additionally, two subtypes for individual plants not associated with the above two populations were also found: one intermediate between type II and type III; one with no ligules, but with peripheral florets exhibiting a long tubular corolla (in contrast to the nonperipheral pistillate florets).

The main differences for the three main types are summarized in the following table.

	I. Travis Co., Barton Creek Greenbelt	II. N Hays Co., adjoining Deadman's Creek	III. N Hays Co., a valley above Deadman's Creek
trimorphic florets	yes
reproduction	chasmogamous	apomictic (?plus chasmogamous)
florets per head	91–106 (avg 97)	36–85 (avg 56)	67–73 (avg 69)
ligules	showy	visible, barely exerted at anthesis	virtually invisible (require microscope)
anther tube of perfect florets exerted	yes	no
corolla tube length of eligulate pistillate flowers	3.1–3.8 mm (average 3.6 mm)	3.6–5 mm (average 4.6 mm)	4.5–6.2 mm (average 5.2 mm)
styles of eligulate pistillate flowers	clearly visible when heads open, not when heads closed	hidden by pappus bristles, but may become visible when darkened in older heads
pappus length	avg. 9.4 mm	avg. 12–12.9 mm
heads open at anthesis	yes; diurnal	no
head ‘nodding’ behavior: in the taxonomic literature in relation to peduncle anatomy
head nodding in bud^* ^*short, conical shaped head on short peduncle	bud initially drooping ±180°; rising as peduncle develops to ±90°
head erect during early anthesis	yes	no; upper peduncle bends down
head nodding during late anthesis	yes, but never to 180°	upper peduncle gradually bends to ± 180°
head angle at dispersal	the entire peduncle straightens to ±erect, with only the very apex tilting downward
head angle at dispersal	20° – 105°	0° – 48°	0° – 24°
peduncle length at dispersal	20–46 cm (avg 33 cm)	5–27 cm (avg 14 cm)	9–34 cm (avg 24 cm)
peduncle cortex asymmetrically thickened	no	yes

Leaves

Althogh I did not initially document the variability noted in leaf form, color and tomentum, subsequent examination of leaf size and form would seem to indicate features that are correlated with the major inflorescence morphology differences noted above for Type I vs. other types. Details to follow.