RELATIONSHIPS OF HOUSTONIA PROSTRATA (RUBIACEAE) OF MEXICO AND ARIZONA AND A REVIEW OF HOUSTONIA SUBGENERA AND SECTIONS

2007·9.4 MB·English

by  Edward E Terrell

AND
RELATIONSHIPS OF HOUSTONIA PROSTRATA (RUBIACEAE) OE MEXICO
AND AND
ARIZONA A REVIEW OF HOUSTONIA SUBGENERA
SECTIONS
Edward
E.TerrelP
Research Associate
Department of Botany
Museum
National of Nat story
urall-li
Smitinsonian
Institution
DC
Washington, 2001 3-701 USA,
2,
ABSTRACT
Houstoniaprostrata, a species discovered in 1899, has been collected in Baja California, Sinaloa, Sonora, Mexico and Cochise Co. Arizona.
,
many
Its relationships have been problematical for years. Comparisons of seed and pollen morphology in Houstonia and Hedyotis species
new
and in Lucya tetrandra support recognition of Houstonia prostrata as the type species of a monotypic subgenus, Houstonia subgenus
named the unique numerous and regularly-arranged pores in the seed Review of previously named subgenera and
Porotis, for testa.
sections in Houstonia indicates that the subgenus Chamisme should be restricted to the Houstonia purpurea L. group of four species. The
group of ten Mexican and southwestern United States species is recognized as Houstonia subgenus Ericotis.
RESUMEN
Houstonia prostrata, una especie descubierta en 1899, seharecogido en Baja California, Sinaloa, Sonora, Mexico y Cochise Co., Arizona.
Sus relaciones han sido problematicas durante muchos anos. Basados en comparaciones de la morfologia de la semilla y del polen en
como un
especies de Houstonia y de Hedyotis y en Lucya tetrandra se concluye que merece el reconocimiento especie tipo de nuevo sub-
genero monotipico, Houstonia subgenero Porotis, nombrado asi por los unicos poros testales numerosos y regularmente dispuestos de
la semilla. La revision de subgeneros y de secciones previamente nombrados en Houstonia indica que el subgenero Chamisme se debe
restringir al grupo de Houstonia purpurea L. de cuatro especies. El grupo de diez especies mexicanas y del sudoeste de Estados Unidos
como
reconoce Houstonia subgenero
se Ericotis.
INTRODUCTION
Houstonia prostrata Brandegee an annual herb native to Baja California Sur, Sinaloa, and Sonora, Mexico,
is
and Cochise County, Arizona. was collected by Brandegee in Baja California Sur in 1899, and no
T.S.
first
It
new known
other collections from Baja are to the present writer. In 1904 Brandegee collected and described
new
another species, Houstonia parvula, in Sinaloa. Standley in treating the North American
(1918), flora.
synonymy
placed Houstonia parvula in under Houstonia prostrata. Shreve and Wiggins (1964) in their Sonoran
Desert flora treated the two species as varieties: Houstonia prostrata var. prostrata with branches prostrate,
internodes shorter than leaves, leaves mostly sessile, and var. parvula with branches erect, internodes mostly
My
equaling or exceeding leaves, leaves mostly short-petiolate. study of the types (Figs. 2) and other col-
1,
lections indicates that these differences are minor and overlap greatly, consequently, have not recognized
I
varieties and have treated the two species as one under the older species name. Houstonia prostrata has also
been found in Sonora, and was collected in 1971 in the United States by Mason, Canfield, and Gilbertson
who
found in Guadeloupe Canyon, Cochise Co., Arizona.
it
MORPHOLOGY AND TAXONOMY
new name
In recent years Houstonia prostrata has been treated as Hedyotis vegrandis W.H. Lewis, a under
name
Hedyotis necessitated by a prior use of the Hedyotis prostrata (see nomenclature below).
many
The question of the circumscription of Hedyotis has been a knotty problem for years (reviewed
by Terrell 1996:16). Seed and capsule characters along with chromosome numbers and pollen morphology
are important in the classification of the tribe Hedyotideae and were used in several papers by Terrell and
^Address for correspondence: 14001 Wildwood Drive, Silver Spring, Maryland 20905, U.S.A
109-
119.2007
Bot. Res. Inst.Texasl(l):
J.
no
Journal of the Botanical Research Institute of Texas 1(1)
kEjgf^,
382879
,S
Isotype of Houstonia prostrata Brandegee (US-382879).
Fig. 1.
coUaborators.The seed and capsule characters proved valuable in establishing tribal (Terrell and Wunderlin
2002) and other taxonomic limits (Robbrecht 1989; Terrell 2005) in the Hedyotideae. Extensive varia-
et
al.
tion in seed structure adds to the impression that the genus Uedyotis has been too broadly circumscribed
in the past. Uedyotis subgenus Uedyotis includes its type species, U. Jruticosa L., native to Sri Lanka and
number
southern India. This species and a of similar Asian and Pacific species are recognized by their cap-
sule and seed morphology (Terrell and Robinson 2003). Twenty-one Hawaiian species formerly in Uedyotis
now
were placed in the resurrected genus Kadua (Terrell et 2005). recognize Uedyotis species as having
al.
I
seeds without ventral depressions and with a prominent hilar ridge on an otherwise level or convex ventral
face. In contrast, Uoustonia prostrata has a large ventral depression containing a hilar ridge, consequently,
it
here excluded from the genus Uedyotis.
is
In a molecular study of Uoustonia Church (2003) grouped Uoustonia prostrata with Stenotis, a genus
with seven species in Baja California (Terrell 2001, formerly in Uedyotis), and the monotypic genus Carterella
(Terrell 1987). The molecular data disagree with the current morphological data on Stenotis and Carterella,
which are so different in morphology from H. prostrata that do not mention them in the present study.
I
Church concluded that the phylogenetic placement and taxonomic status oi Uoustonia prostrata "should be
am
more
reviewed thoroughly before including in Uedyotis or in agreement with this statement
Stenotis.''
it I
Terrell, Houstonia prostrata, subgenera and sections 111
Isotype of Houstonia parvula Brandegee (US-571999).
Fig. 2.
and believe that both morphology and molecular data are important and should be utilized in taxonomic
studies.
Comparison of Houstonia prostrata seeds with seeds of previously examined Hedyotideae revealed only
three genera having hilar ridges in ventral depressions. These are the following: the Asian genus Neanotis
(1)
)
(2) Lucya, a monotypic genus of the West Indies, (3) Houstonia, a genus of 20 species occurring only in North
America
(Terrell 1996).
Neanotis was compared with Hedyotis (sens. incl. Houstonia) by Lewis (1966). He found that Ne-
lat.
anotis pollen was 5-12 aperturate, whereas Hedyotis pollen was 3 or 4 aperturate. He also listed five other
differences in the pollen of the two genera and concluded that Neanotis was fully distinct from Hedyotis. His
conclusions are accepted here.
112 Journal of the Botanical Research Institute of Texas 1(1)
The second genus comparison with Uoustoniaprostrata the monotypic genus Lucya (Table Lucy a
for
is
1).
tetrandra occurs on rock outcrops and similar habitats in Puerto Rico, Cuba, Dominican Republic, Haiti, and
cm
4-25
Jamaica. readily distinct from Houstonia prostrata in habit and aspect, and in being perennial,
It is
with tubers and ovate or elliptic leaves, compared with H. prostrata, a low inconspicuous annual with
tall,
oblanceolate or linear leaves (Table The seeds o( Houstonia prostrata (Fig. 3) and Lucya (Fig. 4) are similar
1).
in having thickened involute (rolled) margins, in being longitudinally bowed, and in having a large ventral
They
depression. differ in the following: Lucya has only a scar in the ventral depression instead of a hilar
(1)
ridge, a testa lacking pores, whereas H. prostrata has numerous pores, (3)6-8 calyx lobes, a marked
(2)
departure from the usual 4 lobes in all other studied taxa of this tribe, (4)6-colporate pollen compared to
3 or 4 in Houstonia species based on recent data supplied by the palynologists Walter H. Lewis and Joan
(
Nowicke). These significant basic differences lead to the conclusion that Lucya should be maintained as a
genus distinct from Houstonia prostrata. The seed similarities suggest, however, that the two taxa are rather
closely related.
A
brief description of Lucya and nomenclatural data are added below in the taxonomic treatment.
its
Houstonia, the third genus with seeds similar those of Houstonia prostrata was monographed by
to
A
Terrell (1996). full comparison of H, prostrata with Houstonia is presented in the following review of the
infrageneric taxa in Houstonia,
INFRAGENERIC TAXA OF HOUSTONIA
This genus has two subgenera and four sections as follows: Houstonia subgenus Houstonia with sections
A
Houstonia and Mullera and subgenus Chamisme with sections Amphiotis i=Chamisme) and diagnostic
Ericotis.
key to these taxa was provided by Terrell (1996: 20-21). The seeds of several of the species mentioned here
The below
are illustrated in Terrell (1996: Figs. 1-4). infrageneric taxa are considered in their order.
much
Houstonia subg. Houstonia includes six species that are distributed throughout of the eastern
United States, southeastern Canada, and southeastern U. south to Florida and eastern Texas. The type
S.
species is H. caerulea L., the traditional Bluets. They all have a similar aspect or habit, and are small herbs,
soft-stemmed, spring-flowering, and with salverform Section Houstonia with species has
corollas. five
(1)
subglobose seeds each with a circular orifice opening into a subglobose hilar cavity lacking a hilar ridge,
(2)
A
chromosome
pollen 3-aperturate, x = except 7 in H. procumhens Gmel.) Standi.. sixth species,
(3) 8, (J.F.
H. rosea (Raf.) Terrell in section Mullera, differs in having seeds with a hilar ridge in a shallow depres-
(1)
chromosome number x = chromosome and from Lewis
sion pollen 4-aperturate, 7 (the pollen data
(2) (3)
chromosome
1962, 1965). Houstonia procumhens differs from other species in section Houstonia in having a
number of x = 7 and capsules widely dehiscing and sometimes separating into two halves and deflexed to
the base of the capsule. Church and Taylor (2005) in molecular studies found that H. procumhens and H. rosea
were genetically quite distinct from other species and are more closely related to each other than previously
known. Houstonia procumhens tetraploid, H. rosea diploid. The data suggest that would be more accurate
is
it
to include H. procumhens with H. rosea in the section Mullera, and this done in the following taxonomic
is
own
treatment. The subgenus Houstonia with two sections hybridizes somewhat within subgenus
its its
&
(Church Taylor 2005), but quite distinct from other Houstonia subgenera and sections.
is all
Houstonia subg. Chamisme section Amphiotis (= section Chamisme) typified by H. purpurea one of
is L.,
four perennial spring- and summer-flowering species with fibrous stems, funnelform corollas, and a chromo-
some number of x = 6. All species have seeds with a low hilar ridge in a shallow depression, entire margins,
and and The
a reticulate testa. Pollen is 3-aperturate colpororate (Lewis in Terrell et al. 1986). distribution
much
of the species includes of the eastern U. and a small part of southeastern Canada. This group
S. is
discrete and genetically distinct from other Houstonia species. Church and Taylor (2005) have provided
helpful molecular evidence about hybridization within this group.
Chamisme southwestern and
Houstonia subg. section Ericotis includes ten species distributed in U.
S.
Mexico. They are annual or perennial with corollas salverform, funnelform, or subrotate, and chromosome
a
Terrell, Houstonia prostrata, subgenera and sections 113
8
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114 Journal of the Botanical Research Institute of Texas 1(1)
Fig. 3. Seeds of //oM5fo/?/aprosfraffl examined bySEM. A-B, \)-?,Brandegees.n.,25Sep 7899(GH), BajaCaWfomiaSutX, Mason etaL 3061 (ARIZ), Arizona.
A, seeds strongly longitudinally bowed. B, C, ventral face showing hilar ridge in depression and thickened rolled margin. D-F, enlargements of testa
showing numerous regularly-arranged pores and areoles with low, indistinct walls. Bar scales in microns.
Terrell, Houstonia prostrata, subgenera and sections 115
&
4. Seeds oUucya tetrandra examined by SEM. A-D, Leonard Leonard 12702 (US), Haiti. A, seed showing hilar scar and thicicened rolled margin. B,
Fig.
zigzag areoles below rim on side of seed. C, same, enlarged. D, polygonal areoles on dorsal face of seed. Bar scales in microns.
number (unknown
of x = 11 for two species). Houstonia rubra Cav. the type species, noteworthy for Ion
is its
mm)
(8-41 corollas. Nine of the species have seeds with coalescent areoles that appear as a jumbled mass
of intermixed areole walls (Terrell 1996, Figs 3d, 4d). These seeds are more complex than other Houstonia
seeds, and have the following characters: boat- or cup-shaped seeds with shallow to deep depressions,
(1)
margins entire or lobed and varying from thin and open to somewhat rolled and covering the edges
(2)
of the depressions, hilar ridges sometimes fused with margins one end of the seed, some species
(3) at (4)
have a bilobed sinus at one end of the seed. Seven selected species are shown in Table 2. Church and Taylor
among
(2005) noted the genetic distinctness these species. The three species headed by H. rubra in
first
Table 2, have generally similar seed morphology. Houstonia humijusa (A. Gray) A. Gray is noteworthy for its
&
symmetrically lobed seed margins. Houstonia acerosa (A. Gray) Benth. Hook. and H. wrightii A. Gray
f.
have cupulate seeds, but otherwise are rather distinct from each other. The seventh species, H. parvijlora
— —
—
- '' ' '
116 Journal of the Botanical Research Institute of Texas 1(1)
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Terrell, Houstonia prostrata, subgenera and sections 117
Holz. ex Greenm., endemic to southeastern Texas, differs from the others in having reticulate testas and
chromosome
polygonal areoles, however, other characteristics, including number, resemble the other
its
nine species. Pollen in section Ericotis is 3-colporate and colpororate (Lewis in Terrell et al. 1986). The group
among
includes considerable variation species but fully distinct morphologically and genetically from the
is
other subgenera and sections.
The previous discussion of Lucya compared H. prostrata (Table concluded that the two taxa are
to
1)
similar in two unusual seed characters, but have basic differences in pollen and calyx lobes; consequently,
Lucya remains monotypic genus.
a distinct
Two
Gray and
of the section Ericotis species, H. suhviscosa (A. Gray) A. H. parviflora, differing in their
seed morphology, are included in Table for direct comparison with Houstonia prostrata and Lucya tetrandra.
1
among
Several morphological characters are rather similar these species (see also Table Nine of the sec-
2).
tion Ericotis species have seeds with coalescent areoles, a character absent in H. prostrata. The tenth species,
H. parvijlora, does not have seeds like H. prostrata.
concluded that the general resemblances of Houstonia prostrata are to Houstonia, has a seed
It is e.g., it
with a ventral depression containing a hilar ridge and 3-colporate pollen. has other resemblances as
It
documented The
in the tables. specialized characters peculiar to H. prostrata are the following: seeds
(1)
longitudinally bent, margins conspicuously thickened and involute, testa with numerous conspicuous
(2) (3)
regularly-arranged pores. (The two of these characters also occur in Lucya tetrandra). The presence of
first
numerous pores in Houstonia prostrata considered especially significant, as pores have never been found
is
new
in any other hedyotoid genus studied thus Houstonia prostrata a clearly marked and distinctive
far. is
subgenus of Houstonia, here termed as subgenus Porotis emphasizing unique testal pores. The following
its
paragraphs document nomenclatural and taxonomic
characters.
its
TAXONOMIC TREATMENT
The preceding outline of the subgenera and sections follows the classification devised previously (Terrell
1996), however, has become apparent that the sections Amphiotis (Chamisme) and Ericotis are fully distinct
it
and do not belong in the same subgenus. had in 1991 treated Ericotis as a subgenus, and this combination
I
appears below as a restoration of an earlier combination. The four subgenera are listed below. Sections are
recognized only in Houstonia subg. Houstonia.
1. Houstonia L. subgenus Houstonia, Sp. Pi. 1:105. 1753. Lectotype: Houstonia caerulea L. Six species. Section Houstonia
witli four species, Section Mullera Terrell with two species.
Chamisme
2. Houstonia subgenus Rafinesque, Ann. Gen. Sci. Phys. 5:227.1820. Lectotype: Houstonia purpurea
Four
L. species.
Houstonia subgenus Ericotis Phytologia 71 1991
3. Terrell, :2 19. Type: Houstonia rubra Cav. Ten species.
.
Houstonia
subgenus Porotis
4. Terrell, subg. nov. Basionym: Houstonia prostrata Biandtgtt, Zoe 5:105.1901. Type: Houstonia
prostrata.
mm
Plantae parvae herbaceae annuae; corollae 1-2 longae tubulares; capsulae 3/4 inferiores longitudinaliter dehiscentes; semina
longitudinaliter curvata cymbiformia margine involuta, hilis linearibus in cavis prominentibus; testa in parietibus cellularum minute
multe
porifera.
mm
Plants small annual herbs, corollas 1-2 long, tubular, capsules 3/4 inferior, dehiscing loculicidally,
seeds longitudinally bent, cymbiform, margin involute, linear hilar ridge in a ventral depression, testa with
numerous minute
pores.
—
name
from and
Etymology. Porotis is a derived poro, pore, -otis, ear.
HOUSTONIA PROSTRATA
Houstonia prostrata Brandegee, Zoe 5:105.1901. Hedyotis vegrandis WH. Lewis, Rhodora 63:222.1961, nom. nov., non
&
Hedy prostrata Korthals, Nederl. Kruidk. Arch. 2:160.1851. Houstoniaprostratavai.prostrata'Wiggms in Shreve Wiggins, Veg.
Otis 2,
MEXICO.
Fl. Sonoran Desert 2:1399.1964. Type: Baja California Sur: on clean sand of dry stream, resembling a prostrate Euphorbia,
La Palma, Cape Region, 25 Sep 1899, T. S. Brandegee s.n, (lectotype: UC!; isotypes: GH!, NY! US-2!). (Fig. 1 isotype US-382879).
118 Journal of the Botanical Research Institute of Texas 1(1)
non
Houstonia parvula Brandegee, Zoe 5:221.1905, Hedyotis parvula (A. Gray) Fosb., Bishop Mus. Bull. Bot. 174:54.1943. Hedyotis
&
sinaloaeW.U. Lewis, Rhodora 63:222. 1961, nom. nov. Houstoniaprostratavar. parvula (Brandegee) Wiggins, in Shreve Wiggins,
MEXICO.
Veg. Fl. Sonoran Desert 2:1399.1964. Type: Sinaloa: Gravel deposits of Tamazula River near Culiacan, 12 Oct 1904, TS.
Brandegee s.n. (lectotype: UC!; isotypes: GH-2!, MO!, NY!, US-2!). (Fig. 2 isotype US-571999).
cm
2-9
Small annual herb (Table Stems slender, erect or prostrate and matted, minutely whitish
tall,
1).
mm,
5-14
papillose-puberulent to glabrate. Leaves x 0.5-2,5 sessile or short-petiolate, narrowly oblanceo-
late, linear, narrowly elliptic, or narrowly oblong, minutely papillose above, glabrous or minutely papillose
mm
mm,
beneath, margins often revolute, apices obtuse or acute. Stipules to ca. 1 x ca. 2 scarious, deltate,
margins with 1-few sometimes gland-tipped Flowers apparently homostylous, one per node, subses-
teeth.
mm
sile or on pedicels to 2 long, becoming recurved at fruiting stage. Hypanthium (calyx cup) puberulent
mm
mm,
numbering 1-2
or scaberulous; calyx lobes 4, to ca.l x ca. 0.6 lanceolate or deltate. Corollas long,
mm mm
tubular, white or apices of lobes tinged with purple; tubes 0.5-1.5 long; lobes 0.5 long, usually
ca.
mm
mouth
shorter than tube; anthers 0.2 long, inserted of tube; stigmas included in tube, not
ca. elliptic, at
3-4 mm,
seen. Capsules 1.5-3.0 x wider than long, 3/4 inferior, thin-walled, fragile, 2-locular, glabrous or
minutely papillose, dehiscing widely loculicidally and splitting the septum. Seeds (Fig. 3) 4-10 or more per
mm,
capsule, 0.8-1.2 x 0.5-0.7 black, somewhat compressed dorsiventrally, longitudinally bowed, cymbi-
form, in outline broadly elliptic, elliptic, or oblong, dorsal face rounded, ventral face with a moderately deep
elliptic depression, margin entire or slightly wavy, thickened, involute or inrolled, linear hilar ridge centered
in depression and 2/3-4/5 as long as seed, ridge ends sometimes slightly enlarged, areoles polygonal, with
low, indistinct walls, testa with numerous minute pores (Fig. 3D-F). Terrell (1986 et Figs. 8) illustrated
al., 7,
the pollen o[ Houstonia prostrata with the numerous pores (the contribution of Joan Nowicke), and data sup-
common
plied by Lewis in that paper noted that H. prostrata pollen has colporate type A, the most type in
may
the Rubiaceae and generalized type from which species with more specialized pollen have evolved.
a
The chromosome number Houstonia not known. Flowering August October.
for prostrata to
is
—
Distribution. Stream beds, gravel deposits, llanos; Mexico: Baja California Sur (Cape Region), Sinaloa,
and western Sonora; United Cochise Arizona.
States: Co.,
W
Additional collections. MEXICO. Sonora: Olneya-Prosopis-Cercidium llano, 27 mi of Hermosillo on road to Kino Bay, 28 Aug 1941,
&
UNITED
LL. Wiggins R.C. Rollins 135 (ARIZ! CAS! DS! GH!, MICH!, MO!, NY!). STATES. Arizona. Cochise Co.; in gravel-filled
depression on rock outcrop above stream, Guadeloupe Canyon, in southeasternmost corner of county and state, 25 Aug 1971 C.T. Mason,
,
3061
E.Canfield, R.Gilbertson (ARIZ!).
LUCY A
DC, &
Lucya nom. (ICBN
Prodr. 4:343.1830, cons. 2000). Type species: Lucya tetrandra (L.) K.Schumann, in Engl. Prand,
DC,
Nat. Pflanzenf. 4(4):27.1891. Peplis tetrandra L., Amoen. Acad. 5:413.1759. Lucya tuberosa Prodr. 4:434.1830, nom. illeg.
ICBN
2000).
(fide
This limited description based on 25 collections loaned from herbaria and descriptions in
is floras.
mm
cm
4-25
Small perennial herb (Table 1) with tubers to ca. 7 wide. Stems tall, slender, erect,
mm
5-32 4-17
spreading, or prostrate, glabrous or pubescent. Leaves with petioles to ca. 5 long, blades x
mm,
ovate, broadly ovate, or broadly elliptic, tapering or broadly rounded at base, glabrous or pubescent
mm
to densely hirsute, sometimes with flattened hairs, apices usually obtuse. Stipules to ca. 1-2 long and
wide, apices sometimes with short teeth. Flowers apparently homostylous, usually one per node, on filiform
mm
Hypanthium
pedicels 1-7 long, erect, spreading or in fruit recurved. (calyx cup) glabrous to densely
mm
numbering
hirsute; calyx lobes 6-8, to ca. 1 long, linear or shortly lanceolate, glabrous or ciliate. Corollas
mm mm mm mm
2.0-2.3 long, tubular, white; tubes ca.l long; lobes ca.l long, ovate, glabrous; anthers 0.2
mm,
mouth 3-5
long, inserted of tube; stigmas included in tube, not seen. Capsules 2.5 x wider
elliptic, at
than long, 3/4 inferior, thin-walled, 2-locular, glabrous, sparsely pubescent, or hirsute, dehiscing widely
and becoming 5-8
loculicidally halves completely deflexed. Seeds usually per capsule, 1.4-1.7 x
(Fig. 4) ca.
mm,
0.9-1.4 black or dark brown, somewhat compressed dorsiventrally, longitudinally bowed, cymbiform.
in outline broadly elliptic, elliptic, oblong, or suborbicular, dorsal face rounded, ventral face with a rather