Unresolved Malva In San Marcos

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Unusual Malva pseudolavatera? ("Malva X") From San Marcos, San Diego Co., CA
   © W.P. Armstrong & Steven Disparti
   14 July 2012 Updated 17 Aug 2019
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Brief Synopsis: Flowers & fruit key out close to Malva pseudolavatera; however, smaller flower size & low-growing, spreading (procumbent-decumbent) growth form do not fit M. pseudolavatera. [In decumbent growth form the tip is ascending.] M. neglecta & M. nicaeensis have decumbent growth form and smaller flowers, but epicalyx bractlets of M. neglecta & mericarps of M. nicaeensis do not fit. Is this an unreported species for California & the U.S., or a fertile, ruderal Malva possibly of hybrid origin? See Summary & Conclusions. According to Christopher Davis (personal communication, March 2013), this is a low-growing morph of M. pseudolavatera.
   Important Plant Taxonomy Links     Search The Kew Plant List       International Plant Names Index  
Annual & Perennial Malva Species With Petals Less Than 15 mm Long

The above criteria excludes North American native & naturalized species with larger, showy flowers, such as M. alcea, M. arborea, M. assurgentiflora and M. moschata. Petals of M. pseudolavatera are 15 mm long, but this is an upright shrubby plant, not at all decumbent.

Malva X has the following characteristics which just do not fit the Malva keys in the Jepson Manual Vol. 2 (2012) and Flora of North America by Steven R. Hill:

  1. Growth form decumbent.
  2. Petals 10-12 mm depending on water & soil; smaller than M. pseudolavatera & with paler veins.
  3. Epicalyx bractlets widely lanceolate to ovate; bases fused to each other or to calyx (not like M. neglecta).
  4. Mericarps smooth or faintly net-veined (not like M. nicaeensis).

Table Comparing Major Characteristics Used To Key Out Malva Species
In Revised Jepson Manual Of California Vascular Plants Volume 2 (2012)

Shape of bractlets subtending the calyx &
Extent of calyx lobes subtending fruit.
Calyx lobes spreading,
not enclosing the fruit.
Calyx lobes generally
enclosing the fruit.
Bractlets narrow-linear to threadlike.
M. parviflora
----------
Bractlets widely linear to narrow lanceolate;
free from each other and from the calyx.
M. neglecta
Acc. to illust. in Jepson Manual.
M. neglecta
M. verticillata
Bractlets widely lanceolate to ovate;
bases fused to each other or to calyx.
Mericarp strongly net-veined.
----------
M. nicaeensis
    (Growth Decumbent)    
Bractlets widely lanceolate to ovate;
bases fused to each other or to calyx.
Mericarp faintly net-veined to smooth.
----------
Growth Erect:
      M. pseudolavatera
      
    Growth Decumbent:    
Malva X*; Resembles
Italian M. multiflora**

*Based upon key characteristics in the Jepson Manual On-Line Edition (2019).
**Accepted species in Kew Plant List & International Plant Names Index (IPNI)

Field observations and numerous plants grown in test plots by Steven Disparti clearly show that Malva X develops a low, decumbent growth form. M. nicaeensis also develops a decumbent growth form; however, its mericarps are very different from Malva X. The mericarps of M. nicaeensis are strongly net-veined & pitted on back with sharp outer edges, and they remain tightly connected in wheel-shaped schizocarp. Mericarps of Malva X are smooth to faintly ridged on back, similar to those of M. pseudolavatera, with outer edges +- rounded. Mericarps of Malva X readily separate (shatter). These characteristics are illustrated in the following images.

Based upon information and images on this web page, Malva authority Christopher Davis (personal communication, 20 July 2012) states that "Malva X" is a decumbent growth form of Malva pseudolavatera: "I had a look at your atypically decumbent Malva, which is indeed M. pseudolavatera. This can often happen to Malva species that are otherwise more erect, if the main stem is damaged early on (and this is the typical habit for M. neglecta and M. pusilla). " In addition, Mr. Davis said that M. multiflora is a superfluous synonym of M. pseudolavatera.

Note regarding observations by Christopher Davis: Seeds from "Malva X" grown in test plots by Steven Disparti consistently grew into decumbent (prostrate) plants without any damage to the main stem. See the following images.

  Other Malva Species In San Diego County  

Malva X in field in San Marcos. Growth form is decumbent although main stalk appears to have been cut. The petals are 10-12 mm long. 23 March 2012

Malva X grown from seed clearly retained the decumbent growth form. The plants are vigorous, prolific seed-producers. The petals are 10 mm long. 13 July 2012

Malva pseudolavatera and Malva X growing side-by-side in test plots (24 July 2012). Although their flowers and fruits are similar, their growth form is completely different.

Parental San Marcos Malva X at its original site in San Marcos in December 2012 showing procumbent growth form of dead stems. Numerous seedlings with heart-shaped cotyledons appeared around this parental plant. It will be interesting to see if they also develop the decumbent growth form during the following spring and summer of 2013. See next image taken the following May 2013!

Malva X flowers are pale in color. Veins not as dark purple as in M. pseudolavatera.

A. Malva X. B. Malva pseudolavatera. The petals of M. pseudolavatera are 15 mm long.

Epicalyx bractlets are too wide for M. neglecta.

Fruit segments (carpels) partially covered by calyx lobes.

Calyx lobes of Malva parviflora are reflexed outwardly. Malva X calyx lobes are partially folded over mericarps.

The flowers of Malva X are similar to M. pseudolavatera except they are smaller and lighter in color. The petals are about 10 mm long,

The mericarps of Malva X are similar to M. pseudolavatera. They have faint but visible cross-ridges (net veins) on back, unlike the prominent ridges of M. nicaeensis. They lack the thin-winged, toothed edges of M. parviflora. The outer edges appear +- sharp-rounded. M. neglecta has smooth to weakly ridged segments with rounded edges.

Mature fruit segments (mericarps) of Malva X.

Seedlings of Malva X that recently sprouted from a cluster of seed-bearing carpels.


Malva nicaeensis From Twin Oaks Valley, San Marcos, CA

Decumbent Malva nicaeensis in parched, dry field near horse corrals & track at Walnut Grove Park, San Marcos, CA. The flowers were small (10-12 mm in diameter). Mericarps distinctly reticulate & pitted in back.

Close-up view of flower & fruit of Malva nicaeensis at Walnut Grove Park, San Marcos showing small size of flower compared with calyx and fruit (schizocarps). The distinctly reticulate & pitted mericarps are characteristic of this species.

Comparison of the fruits (schizocarps) and individual carpels (mericarps) of three naturalized annual (biennial) species of Malva in San Diego County. Mericarps of M. nicaeensis are strongly net-veined-pitted on back with sharp outer edges. Mericarps remain connected in wheel-shaped schizocarp. Mericarps of M. pseudolavatera are faintly net-veined or cross ridged on back and with outer edges +- sharp. Mericarps of Malva X are smooth to faintly ridged on back, similar to those of M. pseudolavatera with outer edges +- rounded. Mericarps of Malva X readily separate (shatter).


Malva neglecta From Jerome & Prescott, Arizona

The growth form of Malva neglecta is generally low-growing (spreading), unlike the erect M. parviflora and M. pseudolavatera. Mericarps are finely pubescent and smooth on the back, without distinct pits or net-veins as in M. nicaeensis. The mericarps separate from each other at maturity, unlike M. nicaeensis. Calyx lobes generally do not enclose the mature schizocarp. Epicalyx bractlets are narrow-linear, free from each other and the calyx (unlike M. pseudolavatera). Flowers are white to pale pink with pale veins, roughly intermediate in size between M. nicaeensis and Malva X.


Summary & Conclusions:

1. The epicalyx bractlets of Malva X are widely lanceolate to ovate with bases fused to each other or to calyx, similar to M. pseudolavatera; however, the flowers have paler veins and are smaller. The decumbent growth form is similar to M. neglecta and Malva nicaeensis; however, M. neglecta has epicalyx bractlets that are widely linear to narrow lanceolate, free from each other and from the calyx. The smooth mericarps of Malva X are very different from the strongly net-veined and pitted mericarps of M. nicaeensis. The general flower size with pale veins is similar to M. neglecta.

2. Another interesting revelation is Malva multiflora. The following website has images tentatively identified as M. multiflora that look practically identical to Malva X, including the broad epicalyx bractlets and decumbent (prostrate) growth form. Some on-line references consider this species synonymous with M. pseudolavatera; however, the Kew Plant List (2012) treated both of them as "unresolved." The International Plant Names Index (IPNI) lists Malva multiflora (Cav.) Soldano, Banfi & Galasso with only one synonym Malope multiflora Cav. The IPNI also lists Malva pseudolavatera Webb. & Berthal. with three synonyms: Lavatera cretica L., Malva linnaei M.F. Ray, and Malva hederifolia Vis. Therefore, according to IPNI Malva multiflora and M. pseudolavatera are two separate species! However, according to Malva authority Christopher Davis (personal communication, 20 July 2012) M. multiflora is a superfluous synonym of M. pseudolavatera.

  Images Tentatively Identified As Malva multiflora  

When I checked the Kew Plant List in Aug. 2019, it listed both
Malva multiflora and M. pseudolavatera as accepted species:

   Important Plant Taxonomy Links:     Search The Kew Plant List       International Plant Names Index  

3. Using floral and fruit characteristics along with growth form, Malva X just does not key out in the Jepson Manual Volume 2 (2012) or the Flora of North America.

4. This plant is a prolific seed-producer, typical of a weedy, annual. The original plant was growing in a field near the location of an old grain silo in San Marcos. I have found many interesting naturalized weeds in this area. Seeds from the original location were planted in test plots in Escondido. They all developed into nearly identical decumbent plants with little or no variation in flowers or fruits. Could this be a fertile hexaploid hybrid ("ruderal malvoid hybrid")? See the following article by P.E. Garcia, P. Schönswetter, J.F. Aguilar and G.N. Feliner (2009):

  • Garcia, P.E., Schönswetter, P., Aguilar, J.F., and G.N. Feliner. 2009. "Five Molecular Markers Reveal Extensive Morphological Homoplasy and Reticulate Evolution in the Malva Alliance (Malvaceae)." Molecular Phylogenetics and Evolution 50: 226-239.

    "Among the closely related small-flowered ruderal malvoids, different accessions of M. neglecta do not form a cohesive group, but group either with M. nicaeensis and Lavatera cretica (data not shown) or with M. verticillata. This is probably due to hybridization, a well known phenomenon among the hexaploid small-flowered mallows (M. neglecta, M. nicaeensis, M. parviflora and M. sylvestris), which has caused a high number of names describing the variability and morphological diversity of hybrids (see Sennen, 1910, 1932)."

5. According to Christopher Davis (personal communication, March 2013), Malva X is a low-growing morph of M. pseudolavatera. After studying the growth of Malva X seedlings and comparing them with other Malva species, I tend to agree with Christopher Davis; however, I am puzzled that M. multiflora & M. pseudolavatera are now listed as accepted species on the Kew Plant List. Images of M. multiflora look remarkably similar to our decumbent Malva X.


Addendum: (19 July 2019)

Field Where Malva X Was Discovered: No Trace Of Malva X, But Entire Field Covered With
Naturalized Weed Tentatively Identified As Stinkwort (Dittrichia graveolens--Asteraceae)

Tentatively identified as stinkwort (Dittrichia graveolens), a fall-blooming, naturalized weed in the sunflower family (Asteraceae) native to Europe, Mediterranean, southwest Asia and Africa. I will confirm ID when it flowers in September. This species is considered to be a serious, aggressive weed in San Diego County and especially in California wine country. The stems and leaves are covered with minute, globose, sessile, sticky resin glands and dense hairs that provide insulation against dehydration and allow the plant to survive the heat & drought months of summer & fall. Reported to cause allergic contact dermatitis in some people. Allelopathic effects on other weeds & cultivated crop plants has also been reported.

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